Upvote:1
We can't know for sure, because our information is so scanty about very early civilisations. The two obvious possibilities are:
Humans have an innate tendency to invent explanations for things they don't understand, and to treat them as having personhood.
Rather than being innate, this happened to be a cultural value among early humans, and has been passed down to us since then.
It's extremely hard to distinguish between these possibilities at this distance in time. While experiments could be designed to distinguish between them, they would involve bringing up newborn children without human contact. This is considered profoundly immoral, and thus the experiments should not be done.