Is how God likes to work on us.
Why? Because he is not so much interested in the quickest way to a fixed version of you. Rather, he is interested in how he can grow you closer to him in the process. God loves it when we choose him, and during the slow growth journey he offers thousands of moments to choose him, to trust him. God is awfully fond of your decisions.
Yes, he can fix any issue, foible, or ailment in an instant, and sometimes does. But when he doesn't do things instantly it's because of his goodness, not his stinginess — his beautiful way, not his distance.
PS Most of the things that seem instant have had a lot of build up. If not, they're probably pretty cheap.