A ton of nice guys call themselves/are atheists. About the closest thing to an explanation I can give.
Among arrogant people, atheism seems like a cool thing to brag about because along with making them a minority (so they can talk about how brave you have to be to openly not believe in God, especially in the United States), by its very nature it's based around critical thinking and scientific reasoning. So it tends to attract a lot of assholes who want to feel superior to the common man.
which truthfully it shouldn't even add up to mattering. are you brave for being jewish, christian, muslim? if you think believing (or not) in something makes you brave, then you're not doing it out of personnal conviction, but out of a sense of edginess/ voluntary anti-conformism. believe what you believe and live with it regardless of consequences and leave the real believers to their beliefs rather than making them look bad. i'm not atheist out of a sense of arrogance, i genuinely can't get my head around the concept of a superior entity looking over us. that's why you should call yourself atheist. if you think different, call yourself different (i've got a few bhuddist friends, a couple deists, one agnostic, and so what? their beliefs, not their edginess), it's as simple as that. i wish fundies would learn that, it'd make accepting different beliefs way easier
