"Atheists" covers and awful lot of people so this is only my answer.
I, for one, am not always talking about him. Doesn't usually enter my mind at all on a day to day basis.
However, you may be going on what is posted here. Since one side of the discussion has some fixation of god that is bound to be all over the posts here.
There are, of course, some atheists who are militant about it. Why they are probably is as variable as the personalities involved. Don't start to generalize that is a big mistake.