Why don't some people understand lack of belief?

[Jenny A]

Because people who agree with the OP want everyone to think atheists are just people who go around blissfully ignorant of a fundamental question of human existence, i.e. "Does God exist?" It is question that demands an answer and how someone answers determines whether or not he or she is an atheist, theist, or agnostic. The possible answers are yes, no, and maybe. That's it. Everything else is just evasive puffery.

The question doesn't demand an answer.  For people not brought up in religious homes, the answer is often, meh.  And for people brought up in a theist home, it is not the question that demands an answer, but one's parents.  If the question itself were of such importance, theists would spend more time trying to ascertain which god(s) instead of cozying up to the one  they were raised to believe in.  Which is to say that the question is often more sociel than monumental, even to the casual believer.  

And the answers are: yes; no; maybe; some degree of probable or improbable; I really want there to be and am going to behave as is there is;  and if I say yes, will you leave me alone. Both yes and no can be pretty unexamined.