Being an atheist is the easiest position to take in the modern world. It allows adults to forever be an overgrown child. Atheists think not answering to God means they are so independent valid super ultra adults, and they turn out to be kids who have jobs and don't live with parents. They answer to no one but their whim and the belief system of whatever that is paddled down by the society, and think that belief system is fundamentally superior to religiosity. This is why when society becomes increasingly less religious, you see ridiculously juvenile shit like BDSM+Homo parades, furries, pornography, prostitution, abortion, casual sex, aversion against marriage/family/responsibilities, the list goes on. These are things that overgrown kids do and pursue, they just want to "have fun" and "be their true self" and do whatever they want. What does an atheist have to lose if he is now to become a Christian, or Muslim? He has to stop the worldly enjoyment, control his desires, and live his life not just for him, but for his family, wife, kids, society, and God. There is a lot to gain spiritually for sure, but it's too much for many atheists to confront.
If one is raised atheist, the thought of becoming religious is daunting and they have to change their lives drastically. But a lot do. A lot of people raised Christian or Muslim have an atheist phase in highschool/college years, and realize being atheist should stay just a phase. But I wonder for those who were raised in religious households and become r/atheism level fedora tipper, why do they become so against God? Is it because they really think God don't exist, or do they feel far away from God? Well, the ones I know are overly represented by criminally morally detestable people, probably not truly representative, but it almost feels like they have strayed too far, and terrified of God's judgment, and they cope by yelling God doesn't exist. Or simply they do not want to/can't live up to the standard that God sets, and knows the consequence better than atheists with zero religious background.
But as an honest sperge, I'm confident many exceptional individuals here have an issue with God for true intellectual/ideological reasons. I have been that for a very long time, "umm actually if omnipotent AND benevolent," etc, etc. But as said for forever, religiosity/theology is not on the same level of philosophy/metaphysics, and requires faith. It's much more than just words and arguments. It's also much more than cope, feeling comfy, not wanting to go to hell, etc. All those come as the bonus, not the reason.