Have you ever read these books? From the admittedly very little I've read, they're not in any way, shape or form straightforward enough to constitute actual tenets. That's why nobody actually ever reads them - they offer absolutely nothing in the way of answers or direct instruction.

They do not lay out a belief structure, they do not give rules.

They tell stories that have been transcribed and translated and reinterpreted a thousand times.

And those stories are interpreted, according to the current dogma, by church leadership, into their religious rules of the day.

If the books actually laid out the rules of religion, religious rules wouldn't evolve or change or vary between interpretations - but they do. Constantly. Because the books don't lay out the rules. People do.

The books don't really matter, they're just something those who're making the rules can point to and say "This says I'm right".

(Of course, if you don't belong to a church, you get to decide your own, which is pretty awesome. But it's still you deciding, not the book laying them out.)