Here is my personal take on it. I am pretty sure there is not just one answer here, but I have thought about this personally before. I'm agnostic currently.
As a pioneer, servant, part of the "center" of the congregation, what really got me to leave was through time being able to be honest with things, despite where the honesty took me. I had ZERO desire to leave my religion. I wasn't being mistreated, molested, dealt with improperly (yet).......I just wanted to know what was true and what wasn't. So once i got a question about blood I couldn't answer, and allowed myself to research in a way that wasn't just trying to prove what i already held to be true.....the first brick fell.
that enabled me to think for myself. I followed what I found to be accurate, or in some cases personally meaningful to me, wherever it led me. It led me out of the religion of my youth, despite the high cost.
An unintended consequence, is it made me look into and be honest with myself about things int he bible that don't add up.
Origin of man
The homicidal nature of God
I could no longer just give a pass on these questions. I still question. But the old testemant in particular seems to really just be the writings of an ancient tribal culture justifying its actions through their God. If there is a God and he is loving, he probably doesn't appreciate the bible much. Then again if there is a God and he is loving, and not just waiting out the suffering on earth watching us stumble to improvement through the centuries because of a cosmic bet with one of his sons kids.......you see where I am going here?
I want to believe in more. But just in case I am living my one and only life, I don't want to waste it. And what I do know is that when my loved ones pass......they stop breathing and they are gone. No thinking, no sleep. Just the decomposing of their body that used to hold their thoughts. I have no reason to think I will be any different.