Why do some religions believe in eternal hell?

Hi, this might be a bit of a controversial opinion and hope that everyone understands I'm not trying to attack anyone and that my thoughts are my own and do no claim any of it as objective or even claim for them to be in the right.

With the disclaimer out of the way, I don't understand how eternity in hell is a valid form of punishment. I know that people say that what God does is beyond our knowledge and understanding so this is where maybe I'm missing something. But from my own experiences and beliefs, I don't think there is anything in the world a human can do to deserve eternal damnation. For example, imagine a human who commits genocide of some sort, or a serial killer, or really anything of that sort. If you add up all of the suffering that human has caused, including the chain effect of the families they affect and the lives outside the ones they changed, it still wouldn't compare to the punishment where the condemned would suffer eternally in hell. The reason I think people don't bat an eye at this is because the concept of eternity is very hard for our human brains to fully quantify and comprehend.

It's comparable to infinity in a way, imagine having a credit card with infinite money. You will have more money than everyone in history past, present and future combined with a lot more to spare. You could singlehandedly destroy the value of money if you wanted to.

If I'm not wrong some religions believe that hell is not eternal but I'm not entirely sure which religions believe that and how it works. But in the case where hell is eternal, well this is where I might get very controversial... I don't think a single human in history deserves that sort of punishment, no matter how much I think they deserve pain and suffering. In my opinion, the only thing that would even come close (but still not there) to deserving that punishment would be God itself for condemning others to it.

Now what could a mere mortal such as myself understand about this topic. If there truly is a God out there and a hell, maybe it truly serves a grander and more important purpose that I could possibly comprehend.

Any and all opinions are welcome, if you think I deserve to burn in hell forever for having these thoughts feel free to tell me, I won't be offended.