Generation and nationality enter in to it a lot.
In some countries declaring your atheism is a death sentence, in others it will endanger your career and social standing.
In some countries people could not care less.

In my generation it is still something to be discussed and contended about all be it on a fairly civilised basis. My son however is an atheist, and sees no reason to justify it.
Asked why are you an atheist
I will reply because I see no reason or evidence to indicate a god exists
He will reply Because I am an adult and I'm not a fucking idiot. Grow up.

When I engage in dialogue with Theist he says I am wasting my time talking to morons, I don't agree, but he and his social circle simply don't consider religion worth talking about, assume that one another are non believers and don't let it enter in to their lives.

I feel in the UK at least, in fifty years most of his and the next generation will all simply disregard relgion completly, it take longer among the Jewish and Islamic communities, but even now I see a lot of Muslim young people only going to Friday prayer to kep their father's off their backs and for a quiet life, once that older generation goes they will probably be completely Anglicised.
Among the UK Jewish community many of the Youngsters treat being a Jew as being a member of a club and the amount of people calling themselves Jewish Atheists is amazing.

Well several things go into that. As @AnneWimsey's comment shows, many people are uninterested in talking about it or see it as a conversation that should be avoided. (I personally know that's foolish but to each their own.)

Also, yes. Some are afraid to be open about it. The potential backlash of revealing it is more than they know they can handle. While I'd like to know most people are open minded enough to see past a difference of beliefs, the truth is there are many who can't or simply won't.

I dealt with that struggle myself when I realized I was atheist. My is fundamentalist . Specifically Jehovah's witnesses. As a result almost my entire social network was made up of fellow witnesses. If you don't know much about the JWs, they do is emphasize the need to not associate with anyone outside the church unless absolutely necessary. Such as a work or school related matter and to never befriend outsiders unless it is for the express reason of converting them. If it becomes clear they won't convert move on. Also, if anyone leaves the church they are to be "disfellowshiped"( expelled) from the church and completely shunned by church members and even . When I came out as atheist the majority of friends I had known since childhood immediately turned their back on me and I was disowned by much of my . I had to rebuild my social network almost entirely from scratch and come to terms with the fact that a lot of my that I love may never speak to me again. It's been a rough few years. The experience, a with other compounding factors, left me with depression and anger issues, a with a nice fear of abandonment. things I still struggle with now, years later.

That is my reality and the potential reality of many others and it's terrifying. So understandably many don't want to it.

No it is not as they are afraid to be open about it. It is just that they are way too busy of finding a soul mate, drinking and clubbing, and I am not talking about everybody in your age group, just most.

I think your politics and your religion should be kept quiet, unless of course you are at an anti-Trump rally