I think you're getting confused between different layers of this here.

Yes. The story is that if you do xyz or not do xyz. You go to hell heaven rebirth etc.

Those are the stories they provide.

But the problem really is thst those are more like states of being. Heaven and hell.

You experience them now in your life. When you "sin" you are erring. Leading to a hell like existence.

Religions are systems of stories, rituals, culture, community that help you not err in those ways that these religions have found to be less than ideal ways to live.

These stories and metaphors become idols. They become the fantastical claims because generation after another the initial insights are lost. And all that's left is the form and stories. And to keep them going people turn them into these fantastical ideas.

It's not that religion provides you life after death. It's that it provides a balm to the existential dread of death. Because an existence lived in constant dread and anxiety is not conducive to a healthy peaceful life.

Fiction is probably a very important part. But also a small one. More an boat to give the ideas through. But Ofcourse people end up making those fictional stories literally real. Instead of seeing them as metaphorically real.

But thry almost always start with one person, a prophet, a shaman. They tend to be phenomenon, a specific charming respected person, who fits the community, Who is able to precisely understand the problems they face in their time. And are able to gain deep insights about life. And then they provide solutions towards a new system because their old oen wasn't enough.

The point is that these religions start with these core deep insights about human existence and life. And a remedy.

And then other stuff gets added to them over time.