I don't think it was rejected by all Jews. Didn't they find scrolls of Enoch from the Essence community at Qumran?
Here:
https://en.wikipedia.org/wiki/Aramaic_Enoch_Scroll
I cannot answer your second question, but it is recorded in the Bible this:
Enoch walked faithfully with God; then he was no more,
because God took him away.
I do not think early Christians rejected it. Jude cites directly from Enoch:
14 And Enoch also, the seventh from Adam, prophesied of these, saying, Behold, the Lord cometh with ten thousands of his saints,
15 To execute judgment upon all, and to convince all that are ungodly among them of all their ungodly deeds which they have ungodly committed, and of all their hard speeches which ungodly sinners have spoken against him.
Why do I think it was ultimately removed? Because it makes too much sense...If people had historically accurate accounts then scientific people would be more apt to learn and be curious. As it stand now, you have about 3 Chapters of a boat, animals, floods, and most analytical people are just like yeahhhhh okay. I think there is a group of people and higher beings where it is in their best interest to keep people complacent and unaware of their existence. Paul teaches as much:
12 For we wrestle not against flesh and blood, but against principalities, against powers, against the rulers of the darkness of this world, against spiritual wickedness in high places.