Its like they took a great many science classes, or a couple of philosophy classes, or a single class on logic.
Because it is possible to examine our universe in its splendour, magnificence, 'epicness' and wonder and say, "just because I do not understand how this came to be, does not mean that 'god X' (or any god for that matter) made it."
Simply because you have one explanation that you feel is 'correct' or a series of explanations that you think are 'possible' does not mean that your premises are right, that your reasoning is sound or that your list of potential causes are exhaustive. Theism and atheism alike rest upon belief in their explanations for things; they arrive at their explanations in different ways, but their assumption that the explanation is correct is a belief - some of those beliefs have more or less evidence to support/contradict them, but both are positions of belief.
Your insistence, here and in other threads that atheists are somehow limited in their capacity to comprehend is unwarranted and is more likely to lead to friction in your discussions.
For the record, no I am not an atheist, though some people seem to think so.