Jude may have quoted Enoch to make a point, that is what some think, but others think that the prophecy of Enoch was passed down and was used be the writers of Enoch along with other things the scriptures said about Enoch and filled in their rest of their fable with their vain imaginings. I don't know the answer to that. I believe anyone can read Enoch and discern that it is not inspired or useful, but fables of Greek/Jewish scyncretic sect making up things that the bible does not tell us. Like if someone were to write a fictional novel about Cains life and call it the book of Cain and say that Cain wrote it. 2000 years from now someone would think it was worth including with the library of scripture simply because it was 2000 years old.
If Jude was quoting Enoch to make a point it may be that the false teachers he was lambasting were advocates of the book of Enoch and he was using their own favorite false teachers to rebuke them, much like Paul quoting Epicurean philosophers of Crete to convince those who read them.