Whether you accept it or not, there are some reasons to view the “alien” phenomenon in this manner, from a Christian point of view.
Anyone who has taken the time to research Biblical passages pertaining to the pre-flood world will eventually end up with a few non-canonical books such as Enoch I, that tell the tale.
It’s very strange, reads like a modern scifi novel in parts. But, the conclusion that Noah, perfect in his generations as he was, was saved along with his family and breeding pairs of every kind of animal, due to nearly all Creation on Earth being corrupted by these beings, is difficult to avoid.
Then, going to prophectic passages in the Bible ... as in the days of Noah, so will the coming of the Son of Man be.
All manner of weirdness has sprung up around this, as you might expect. But, the basic belief is not just pulled out of thin air, and finds some validity in ancient Biblical and extra-Biblical texts.
It is also interesting that fragments of the Book of Enoch were part of the Dead Sea Scrolls. Translations abound on the internet.
WELL SAID.