The apostle Paul quotes two secular Greek writers: Epimenides (Acts 17:28 +Titus 1:12) and Menander (1Cor 15:33). No one would suggest those writers should be included in the Bible! This shows that the Bible quote many books that are not - and should not be - part of Canon
I agree with you, that we cannot take the fact that it’s quoted to mean it is scripture. We need to see how it is quoted and Acts 17 and Titus 1 are being used very differently than in Peter and Jude.
First lets look at how Acts and Titus are used…
Acts: 28 For in him we live, and move, and have our being; as certain also of your own poets have said, For we are also his offspring.
Titus: One of themselves, even a prophet of their own, said, The Cretians are always liars, evil beasts, slow bellies.
In the case of acts Paul was using culturally relevant material to appeal to the Athenians. In the case of Titus he is referring to the Cretens and uses their own testimonies to prove his point. The purpose is very clear, and the speaker is in no way authorizing or using or bringing up the content of those sources.
That is not the case for Jude and Peter. Jude is accessing the content of those books. They don’t just quote the Book of Enoch they speak from it’s content, from it's elusive system of beliefs. For example “And the angels who did not keep their own position, but left their proper dwelling, he has kept in eternal chains in deepest darkness for the judgment of the great day. “ 2nd Peter relates the same message. They are not just quoting Enoch they are founding their message on the specific content of the book. The content of their preaching is not found anywhere else in the Bible to that specificity, it comes from Enoch.
So I think the distinction here is that Jude and Peter rely on the doctrinal content of Enoch. But I must also say that Jude and Peter are not directly calling it scripture, so there is that distinction as well. What we can say is that the content of the Book of Enoch informed the theology of Jude and Peter, and they relied on that content to a great measure that may obtain to scriptural level but not necessarily. At the safest we can say there is something important in the content of Enoch that we as Christians should be aware of because Jude and Peter were aware of that content, it shaped their theological understanding, and they found it to be very important to Christianity.