To re-iterate a common theme of mine, there’s only two good reasons for believing anything:
because it’s true,
or because you are better off believing it is true.
I suggest that one or other of these two, and possibly both, does apply in the case of the afterlife, but that’s covered elsewhere, and I can answer this question quite well without referring to them.
As to why people believe things, that’s a whole different question and leads towards a discussion of authority figures and the advertising industry. I cover those in plenty of other places, so we’ll ignore them here too.
Let’s start by acknowledging that Religion is indeed a human creation, although it’s not clear that its ‘only’ a human creation.
Most religions are based on a core of spirituality. I would suggest that spirituality is real - but you can use your spiritual awareness to determine the truth of this statement for yourself. You do have some - it’s part of being Human. Unfortunately many Humans haven’t learned to use it yet.
Yet even if it were true that Religions are merely Human inventions - and even if it somehow impossibly turned out that they contain not so much as a ha’penth of truth, at least concerning the afterlife, we can still answer the question using the second prong.
Placebos are also Human inventions.
Clearly some people believe they work, so they work. Scientists don’t understand why.
If you are dying of cancer and a genuine registered medical doctor gives you a tablet and says it will cure you, would you disbelieve him just because you are part of a test study and you know that 30% of the subjects are getting a placebo instead of the real test drug?
So you believe him.
And your cancer is cured.
And later you learn you received the placebo.
How did your believing in something that wasn’t true harm anyone?
Maybe that’s why people believe.
Or maybe afterlife is true.
Either way - it makes sense to me.
Hope these thoughts help.