I think the answer to your question is easy. However, I believe your path to be extremely difficult.
The simple answer as to why you won't let go is fear.
I know you already know that, but the fact is you see fear holding many people back from many good things. Why does a woman stay with a man who continually beats her? Why did someone I know keep drinking too much, despite the fact they knew it was bad for them, until he lost his family, his job, his life?
There is great comfort in sticking with what we know and are used to even if we know it is bad for us. That's because you know the environment and in its own sick way it is dependable because you know the rules and how to get along in that environment. But if you break away from everying you've always known, what have you got? In many cases, you don't know until you take that road. Not knowing produces intense fear in a lot of people and rather than feel that fear they stay put where they are at.
True change in one's behavior and personality is rare. It takes total commitment and fierce discipline.
You have to trust and love yourself, or learn how.
I know change is possible because....
I've seen people give up bad drugs, too much booze, or too much food and live a healthier lifestyle.
I've seen people give up a mind control religion that hurt people, even at the cost of losing the very people they loved the most.
In all the circumstances where I've seen dramatic shift in someone's life paradigm it was not done alone, but with the help of people in like circumstances.