As so often, you assume that all religions are essentially the same as mainstream Xianity. But even within Xianity this isn't a given. Jehovah's Witnesses don't believe in heaven and hell in the sense of an ongoing reality, or in the immortaity of the soul: they believe that when you're dead you're dead, and stay that way till Judgement Day, when the saved will be raised to physical immortality on Earth while the rest just stay dead and gone.There is a whole tract of religions that don't believe in an afterlife at all, except as a transition lounge between incarnations. And the Northern Tradition, while it envisaged great lives being rewarded with a continuation among the gods, saw the rest as going to a cold limbo whether they'd been good or bad. (Reputedly, one of the reasons they fell for Xianity, which offered heaven to ordinary folk without their having to do great deeds to earn it.) There is some evidence that the classical Greeks shared this view before they picked up the idea of hell from the East.It would seem to me that, if you define heaven as a place of reward where your soul lives with the gods, then you must have a hell, a place of punishment, even if it's only a place without the gods. This seems to be the basic concept behind most religions.
According to Hindu and Buddhist tradition, it just happens: karma is a natural force, souls rise or fall as weights do. You can say prayers for the dead to help them to a better incarnation, but that's like magic, a way of giving reality a push, not an appeal to the gods as it would be in the Xian tradition.
What about heaven and hell without gods? Well, that doesn't work! Who decides who goes where?
I agree, it's simpler. But only in the same way that living alone is simpler than having lovers.I think being an atheist is easier. No gods, no heaven, no hell. Just here and now.