Alot of why people don't believe in God is because they know him so well. They expect him to do certain things and if he doesn't then he is simply not there.
Everyone has their own idea of who and what God is and what he does and doesn't do. Psh even religions differ to a great degree.
So people will just say, God aint there. God isn't there just because you say that and if you don't think God is there because he isn't your mental creation from imagination you need to think again.
No one knows Gods motives or his reasons and God works on his terms.
Let's face it, that's God and there is nothing we can do about it.
Call him a monster or hate him all you want, join forces with the Devil but you can never get rid of God, overthrow him or take his place.
Just have to accept that, that is God and o'well! You may not like him, but he is there.
So good luck all.