1. It's their job, as adherents, to spread the faith. They're doing what they think they're supposed to do, to be a "good ____".
2. They genuinely care about your well-being and think you can't be well unless you are right with God.
3. They are trying to assess your worthiness, because the only good people are followers of their (or some) faith.
4. They're virtue-signalling.
5. They're trying to connect with other believers for validation.
6. They're just being polite, because religious considerations are inextricably entrenched in their social culture.

Did I miss any?

Their religion trains them to spread the disease. That's the Mormon rite of passage for guys. More members mean more money.

They trying to find someone to brainwash.

Maybe, deep down, they have doubts and are always searching for positive reinforcement from like-minded "believers"?

Usually, they really mean well. " Forgive them, dear lord, they know not what they do..."

Fear.

Particularly in the Bible Belt it's a common form of social signaling; the first thing people want to do is know if you go (or would like to go) to their church or not -- they hope you'll join their club or at least a very similar club. They are not generally proselytizing, they just assume you're one of them, because, who wouldn't be, right?

Outside the Land of Nutters that sort of thing stands out more since it's uncommon, but I think it's not too hard to understand. We're a hypersocial, story-telling species, so of course we want to identify and collect like-minded or persuadable people into our tribe, and validate the stories we tell ourselves about ourselves, reality, god, etc.

I also like to point out that fundamentalist Christianity is all about BEING right; DOING right is secondary (if not tertiary, if not ...). So. ahem anyway ... if you have a strong need to be right OR ELSE god will be disappointed, or perhaps judge, or perhaps punish you -- to be right or your fellow religious club members might look down on you -- to be right or else amplify your already substantial self-loathing -- in that situation you are going to treat your beliefs as beacons of truth. And you're going to assume everyone, if only they paid attention and understood the unadulterated wonderfulness of god's exciting plan for their lives, would agree that you're RIGHT about that, too. And Christians, thinking as they do, tend to feel that the more people who agree with them, the more compelling their beliefs are. Because they focus on appeals to popularity, authority, longevity, ancientness and so forth, given that they lack actual substantiation for their beliefs.

The babble tells them to! "Witnessing" and converting are doing gawd's bidding & earn them brownie points.

The more they say it, the more they think they'll believe it and it will be real to them. The louder they are, the more threatened they feel.

I haven't experienced this, but know what you are talking about. Religion is like deodorant. It has a smell that some like and some don't. Just don't try putting yours under my arms.

I think they are half trying to convince themselves. I think tht those who have doubts are the ones who over compensate the most by talking about their beliefs so much.

I think they crave the acceptance of others. I work with a church every Wednesday, and almost every sentence has "God" in it, and not because someone has dropped something. Whereas I walk around letting fly with expletives.

Of course. Christianity is like an infection. It’s their job to get converts. The Jews and Zoroastrians, Hindus, Seiks, Jains, Shintos.... they either don’t take converts or they discourage them. Christianity and Islam actively encourage it.

I'm in Florida and it's bad, but I just spent two years in North Carolina, and that was way worse! I think they are just trying to make themselves believe and if they can convince other people into it, they can affirm their own faith.

I really think a significant amount of the time it's because of self-consciousness. They know deep down they are just copying what's popular.

Think about it from this perspective. For centuries, the church had the power to persecute people, torture them, kill them, take their land so that their families were left with nothing after they were gone, and much more, if they didn't believe. It became ingrained in Western culture to make sure that EVERYONE knows and there's no question about it, out of fear of all those terrible things. The behavior carries on today as a result of centuries of fear and cultural brainwashing.

Like you I find that aggravating, Salvation Army at Christmas with their Bell Ringers hustling for money and I always wonder how much of that actually goes towards helping people. I would complain to corporate and most will take steps to discourage this behaviour if it is affecting their bottom line by scaring off would be paying customers.

These loons think they are 'saving' people. Those Mormons can ESPECIALLY shove it, speaking from a woman's perspective. Blech.
I was at a flea market buying something, minding my own beeswax, and the guy was ALLLLLL trying to convert me. So I started to debate him. Much to my pride, my fundi sister said to him "OH, my sister really KNOWS her Bible!" There's a funny meme - can't find it now but it says "I sent me down to Earth to save you from me." Summarizes the whole religion.

I have no clue, I have at least fifteen relative's aunts, cousins, second & third cousins that are all hard core believers. Four of them are constantly posting their faith on FB, god is bringing my child home, god is great, praise the lord etc. I have to give them credit though, they have never tried to push their shit down my throat, my stepfather on the other hand was an asshole, Sunday school, then church then Sunday school again

Why not? They have as much right as anyone to voice. Don't you?

I think its just hardwiring that has set solid, I doubt that anybody who does it has any inkling of their own personal process behind it - probably a bit like us Brits sayign 'Hallo nice weather for ducks?' when it rains - to all and sundry- One is religious based one is socal nicety but I think at base -Its just a greeting ,probably said so many times that its meaningless to all parties.

Because the entire purpose of religion is to spread the word and recruit. I absolutely hate hearing it.

Sometimes I think they've been programmed and think everyone is just like them. At other times I think they're trying to run from their own doubts.

The need to because they don't really believe it. It is part of their self brainwashing. I am not kidding in the least. It's like having a great need to affirm your confidence that the sun will rise tomorrow. You don't do that, you don't need to.

Also, depending on the denomination, the pressure to proselytize can be very high.

I'm fucked if I know