It is not in the official Jewish Bible (Tanakh) either. So the Christians and the Jews both rejected it as God inspired, i.e., through prophets.
Reasons To Question The Book Of Enoch:
(1) It is not in the Bible.
God, through His providence, did not inspire those that collected and chose the writings for the current Bible to include the book of Enoch. Thus, one would conclude that God did not want it in the Bible.
(2) It is not in the Jewish Bible.
They also rejected it as not given by a prophet, inspired by God. Romans 3:1 says that
"the Jews were entrusted with the oracles of God". In my view, through God's providence, the official Jewish cannon can be trusted as God inspired as well, according to Romans 3:1.
(3a) The older section of 1Enoch is estamated to be written around 300-200 BC
and the newer sections (it was written by multiple authors) around 100 BC. This falls firmly into the time period when God had
stopped sending prophets (for reasons given below). This period is called the "400 silent years", the intertestamental period of the OT and NT.
(3b) It was written by multiple
authors
The book of Enoch was not written by Enoch but by multiple authors. These multiple authors didn't even have first hand accounts of Enoch or his teachings. This would be ok if they were prophets given inspired knowledge like Moses had (see 3c).
(3c) The multple authors are unknown
During the Old Testament period, those claiming to be prophets had to show signs or give prophecies or interpret visions to show they are sent by God. 1 Corinthians 1:22,
"For Jews demand signs and Greeks seek wisdom". If a person claimed to be a prophet of God and wasn't...they killed them. It would seem very suspicious that the authors of the book of Enoch kept their names hidden. They knew full well they would be killed for claiming to be prophets when they were not. Clearly they were not prophets since it was written during the silent period and God did not make sure the book of Enoch was in the Jewish Tanakh or the Christian Bible.
(4) The condition of the Jewish people when the book of Enoch was written
The reason the time period is called the "400 silent years" is not just because God didn't send any prophets during that time period but also because of the condition and false beliefs of the Jewish culture. Within the Bible one can find a problem of outside beliefs about evil sprits and demons seeping into the Jewish culture. God frequently chastised the Jewish people within the Scripture. This problem of outside beliefs infiltrating the Hebrew cutlure was so rampant leading up to the collapse of Judah that God sent
"His servants the prophets" (Jer 25:4) to warn the people regarding their false beliefs about spirits, demons, and gods. But they would not listen.
God, within the biblical text, accuses the Jewish people of going after other gods to
“serve them and worship them” (Jer 25:6). In Ezekiel, written around 586-538 BC, the leaders are accused by God of setting
“up their idols in their hearts, and put before them that which causes them to stumble into iniquity” (Eze 14:3).
So this was the condition of the Jewish culture during the last prophets God sent and before the NT and Jesus. The book of Enoch was written during a time that God had given the Jewish people over to conquering nations for their false beliefs in demons and evil spirits and their worship. Even during King Jeroboam’s reign in Judah,
“he appointed for himself priests for the high places, for the demons, and the calf idols which he had made” (2Chr 11:15 NKJV).
(5) It is contrary to Biblical scripure and Biblical reasoning
The Bible tells us who we may expect to see as foriegn to earth, that is
fallen angels (Rev 12:4). And gives clues to who these evil spirits and demons are...
angels = spirits&demons (Heb 1:13-14,Matt 12:24-26,Eph 2:2,Psa 104:4,Num 27:16)
demons = spirits (Luke 10:17-20, Matt 8:16, Luke 9:39-42)
angels = spirits & demons
Here is an essay on the topic
Angles_On_Earth.pdf or it can be found online
Demons & Evil Spirits On Earth: A Biblical Account Of Satan And Demonology
May God do a fruitful work through you