One of the primary reasons God in the Old Testament demanded sacrifices of animals is to prove a point. Most pagan religions, particularly the Egyptian one, either revered animals or were part animal in their visualization of their demon gods.
Christians will slaughter every cow in India one day and have beef tacos when they convert from demon worship.
See chapters 6-8 - https://www.bibleword.org/wp/Enoch.pdf
"the Watchers" I believe were angels, but they could, I suppose, have been alien beings that breed with women and provided the basics of scientific knowledge.