I have minor issues with what you've said here. Evolution and gravity themselves are undisputed scientific fact. Theories of evolution and gravity are theories on how these things work.

Now that's out of the way, the answer to this question is simple. Education and tradition. Europe has undergone increasing amounts of secularisation and is becoming less and less religious every decade. Why? Well, it's simple. Europe is the most prosperous continent in the world, especially its western half. Its citizens are well educated and, by world standards, wealthy. Cutting edge science is investigated in Europe, rivalled only really by China and the USA. Many of the world's best universities are in Europe, especially in the UK. Finally, of all the continents, Europe has had the longest history of religious persecution. We're sick of it.

The Middle East is bound in tradition. Certain countries are starting to modernise and, to an extent, westernise, but in countries like Saudi Arabia, Islam is the state religion and is enforced vigorously. The USA isn't bound by law, but it's home to the former British Empire's most religiously extreme colonists; 200 years, and that hardline approach to Christianity still continues. It's funny, really.

People are indoctrinated into religion at an early age, so it is easy to continue to believe. I also believe that most people want to believe in a god, what Did Camus called humanity, spiritual centaurs, forever asking the universe for answers and never getting them

They inherited it from there parents. It's hard to break out too. I did and I get shun for it. I have 5 kids and I'm try real hard to have them be freethinkers.

Herd mentality accounts for 80% of it. The other 20% are the non-believers.

I think there are more people that do not believe in god but are afraid to admit it because society had programmed into it or they are afraid their friends will think bad of them. Many people think atheists are satan lovers. It also makes people uncomfortable when you tell you are an atheist. They do not what to say.

Tradition is part of it. For many they cant' imagine that people would be able to believe somethign for so long and that it would have no actual truth to it

Also, as I have said in many other answers, we evolved in communities and humans are social animals. We have an innate need to be a part of a community and to have a sense of belonging. At one time this was needed for survival, and we may devolve to a point where we need those instincts again, but that need for belonging is an innate instict that is a part of our species.

Religion fulfills the need for that sense of community and that sense of belonging. Even if a person doubts or doesn't really believe, they will put up a front of a solid belief just to fit in and belong. I will go so far as to say that the most rabidly assertive believers are those that have, on some level, the largest doubts and their overt actions to demonstrate belief is a cover up... not just to convince others, but more often they are trying to convince themselves.

Religion is adult thumb-sucking.

I don't think the majority believe in God. I think most of them go along with it so as not to be ostracized or in hopes that maybe it is so and they get to live forever. And most of those don't want to think about if it is really so. It is too scary for them. They just tell themselves, "Sure, there's a God," and move on to other thoughts.

I think that one major factor is that life is so unfair and often heartbreaking that believing that you can have some control over outcomes by being able to reason with an all-powerful, perfect, loving being and convince him/her to make things better is very comforting. It gives an illusion of control, or at least influence.
Also, there's definitely a huge social pressure. Atheists are openly villainized, maybe because of people's fear that we'll take away their suspension of disbelief and they'll lose the thing that makes them feel in control.

I think people use their belief to comfort themselves in a scary confusing word

It is simply the default position for when humans don't have a scientific answer for something. As a lot of the world does not get the benefit of a great education, they default to the gods for answers. Not dissimilar to Romans, and even in Roman times there were the skeptics and atheists.

I don't think it is explained by any one reason; rather, by a few important ones. Deeply entrenched cultural indoctrination is a "how" answer, of course. But "why" seems to be a combination of fear of death, desire to feel we're "special" in the universe, gullibility, and a discomfort with lack of answers about life, death, and the world that leaves many people easy targets for the "Candy Man" appeals of charismatic manipulative individuals who offer cutely packaged, concrete answers; promises of "the Truth."

Fear!

I think a lot of people need to , that aspect is missing in my life and I'm a person that would be happier if I believed in a god but I cant.

1. God provides comfort to the everyday lives of regular people
2. Belonging to a community such as a church, mosque, synagogue, etc. allows people to feel comforted and it meets the requirement for conformity and social interaction
3. They do not desire to contemplate matters beyond their individual understanding because this would require intelligence and understanding of multiple complex topics (too much work for the everyday person)
4. Indoctrination as others have said is an important part of keeping the number of believers high

There is also the meaning and purpose of life which is only attainable after a crisis of faith and a complete rearrangement of an individual's beliefs. This stage is far beyond religion which is why most people break down and then "find God". Because the road to the meaning and purpose of life has a suicide rate of about 99.999999999999999999999999% if you understand the notion which I am implying.

Fear+wilful ignorance, I guess

It's convenient. Some of the music is pretty good. It's a scapegoat for someone to blame the bad stuff on, and a imagined comfort to supposedly help get people through. Many have a social network of like minded make-believers. Many don't want to be the non-believer one in the family. It's their ticket to that imaginary cloud place. One can feel all blessed n' shit.

Brainwashed from birth with religious ideology is why, in my opinion, many still believe in God.

Some have a need to feel they have a purpose, that their task is to be kind and helpful. It's an old question...What is the meaning of life? Organized religion has used that to impose rules and take over the responsibility of establishing moral and values on communities. Hense the ten commandments and all the sins they've made up to control their congregations. Believers get comfort in "their" knowledge of an afterlife with all the family and friends they will be reunited with. This makes them compliant, and a compliant person is easier to use and abuse.

People still believe in God because the delusion costs them nothing, yet makes then feel good about their future, or lessen their fears of death. The belief in God has no real costs because they act as though they were atheists in their daily life.

They’ve had it brainwashed into them. They’re afraid to think for themselves. They’re afraid of death-believing in an afterlife comforts them in times of grief and tragedy.
I always think what the hell would you do there for eternity. It’s a long time to kill.

Knowing how the universe and life works takes hard work. I have honed my opinions and thoughts through countless hours of reading and exposing myself to any information I can. Most religious people don't read anything including the bible. They are basically lazy people who would rather be told what to do and how to act. I have never met a lazy atheist. They want answers and will seek them out.

When you say the majority of people you are likely talking about middle age and older folks. It all goes back to what you were taught as a child by your parents and how stringent that teaching was. Many religious people who are older now have doubts but fear questioning their religious beliefs late in life because they have too much invested at this point. Imagine buying into a system and following it for most of your adult life and someone comes along and tries to convince you that all you have been taught is completely made up and the rules have been changed just when you are going to get your shot at heaven.It is a much easier sell with someone who never had the serious religious teachings as a child.Evolution is a universally accepted scientific theory now accepted as fact and not to be confused with the lesser common term theory..

world wide that may no longer be the case. Don't forget the chinese have had religion removed by force and they represent 1/5th the population