I think it is more that other people give them the title. Most people seem to need a label so they know how to deal with you. Perhaps when asked what religion they are it is easier to say atheist than a long explanation.

As long as Atheists are a small minority they will be described this way. Does a person who believes the Earth is round describe themselves as a round earther?

Religion is a major component of culture. Frankly, I try and not mention it; but if asked (or I get into a situation which would require hypocrisy, which is one of my personally defined "sins") I will say atheist because it describes my religious views quickly and simply. Calling it something else doesn't change my beliefs or how people view me, so, why bother. Sometimes people will try to engage me in debate about it; but I find it is best to keep things simple. Sometimes some folks will try to "save" me; but usually when I tell them I'm not interested in being saved they stop.

Frankly, unless I bump up against a bible thumper, I don't find myself ever having to identify myself as an atheist. So unless someone is trying to make a believer out of me I don't feel it is necessary to describe myself in terms of what I don't believe in. Nor do I find it necessary for them to identify themselves in terms of what they "do" believe in. If a marauding band of Fairi-est corner me and attempt to foist their beliefs on me, I will, of course, be forced to declare my A-Fairi-est status.

I think it's fine to describe yourself in either negative or positive terms... in that sense I am an "a-fairyist". What matters more than the "polarity" of the definition is how one treats self-definitions in general. I am a programmer. That's a self-definition. But, it's also an abstract category that cannot hope to contain everything meaningful I could say about myself. In addition, it's a bit distorting to use "I am" in such a context, because there are "ontological presumptions" in such statements. It would be more precise to say "I write software for a living" -- to describe it in terms of activity rather than identity. But all that gets pretty picky, so conventionally we just keep it simple and say "I am an atheist" or "I am a theist", etc. Where that becomes troublesome is when people start thinking that those categories deserve the same kind of defense and promotion that one should reserve for their true self. If someone threatens my belief or disbelief in God, that is not the same thing as someone holding a gun to my head -- but many people behave as if it were similar, and react with similar protective knee-jerk responses. Beliefs do not define who we truly are. That is the crucial difference between someone who is abusing beliefs, vs. someone who understands the limitations of beliefs.