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.
Considering that no one has ever factually seen an alien, we’re left with nothing but our ability to imagine them. And in times past, we didn’t have big budget imaginations like we have now. So like all things from the past, even our fantasies were basic in comparison.
Ever wonder why no one claims to have seen little grey men anymore? Or for that matter- when was the last claim of alien abduction?
It’s because it’s all bullshit.