I’m wondering if it’s pseudo religious with humans being created in God’s image (Ancient Aliens stuff), the human-centric idea that intelligent life must resemble us, it being easy to make costumes for movies and TV when all you need to do is paint someone’s skin, or if SciFi writers were going for the uncanny valley effect for example.
Maybe https://en.wikipedia.org/wiki/A_True_Story from the 2nd century - although even that is a parody of existing stories. So the origin dates back a long time!