For a very long time, the dominant church forbade the common people from reading scripture. The clergy usurped, for themselves, the sole authority to read scriptures and tell the common people what it said. What they claimed that it said, rather. What could possibly go wrong with that?
It probably has a lot to do with how so many blatantly heretical practices, teachings, and traditions got so deeply rooted into Catholicism, in particular, and remained in the various sects that broke off therefrom, even after people had access to the Bible that should have told them that these things were wrong.
I strongly recommend a video series called
Fires of Faith, that covers the conflicts and efforts that led up to the publication of the King James Bible, martyrs who gave their very lives to make it happen.