Enoch was left out of the bible, because it was never in the bible.
That many Hebrews and many early church fathers had this book doesn't mean there was some conspiracy to omit it. There are many books in this vein, such as the book of Jasher, that were widely held but omitted for simple reasons: they contradicted the rest of what was recognized as scripture by the Apostles, Christ himself, and early church fathers, and they were never recognized as inspired.
The book of Enoch says, among other things:
Enoch and Noah were contemporaries. Scripture tells us that Enoch was translated 69 years before Noah was born.
The book makes Enoch into an intermediary between angels and God, there is no such relationship in scripture.
Enoch says a being named Gadreel was the deceiver of mankind, the Bible tells us it was the great Dragon, that old serpent, the Devil, Satan.
Enoch has what it claims are righteous people praying to angels, something scripture forbids.
Enoch says angels built the ark, scripture makes it plain that Noah did.
Enoch claims it rained before the flood, scripture says it did not.
Enoch enters the Garden, in spite of scripture saying God placed an angel there to guard it that men might not enter ever again.
Jasher is just as bad. It calls Enoch the ruler of the Angels as opposed to Christ, claims Abraham's call was at age 50 instead of 75, claims it was 3 angels that visited Abraham rather than 2 angels and the preincarnate Christ, etc.
It's not a 4th century conspiracy that kept Enoch and other books out of canon. It was what was written in those books. Inconsistencies and errors.