I've asked myself the same and find that there are different kinds of atheism.
There's the "scientific atheism" which regards the existence of gods as just another statement about reality and finds it false.
Another kind of atheism often gets overlooked because you don't find it on its own but only coinciding with "scientific atheism". Let's call that "ethical atheism". Belief in a god doesn't just mean believing that such an entity exists but also pledging allegiance to it and obeying its commands. Most "scientific atheists", in my experience, believe in human rights, democracy and all that. They're also humanists. Even if they received solid evidence of a god, they would still not commit atrocities on its command.
That kind of scientific/ethical atheist pretty much never lapses because the change is just too big, requiring abandonment of rationality and ethics.
Another kind of atheist is the "angry-at-god" atheist. That's the believer approved kind and is usually temporary. They see all the evil in the world and can't believe that a god would allow this. Clearly this is just fallacious wishful thinking. Without a rational or ethical foundation, their opinions shifts with their moods. More generally, when someone justifies their atheism with fallacious arguments, that's the type that will find god sooner or later. And perhaps all sorts of woo.
Finally there's, let's call it "religious atheism". Sometimes you encounter new agers, woo-woos, who believe in all sorts of nonsense but not god. I have no idea what goes on inside these people.
Eventually, atheism is just about what one is not. It says nothing about what one is.
