Why dont some people grow out of believing in god?

Because its something you believe in youre entire life. Its faith. Anyone can believe in Santa Clause their whole life it they want to whether there is proof of him or not. There is no proof that God isnt real. If you have been raised in Christianity, you have choice that when you grow up to believe in it or not. Its not something to make little kids happy, its a religion, and its better than believin in nothing at all.