1. For fun?
2. Because he is not a good God?
3. To teach us a lesson.
4. Because he wants more believers?
5. Because of some plan we will never be able to understand?
6. To teach us a lesson.
7. Maybe Satan and God were somehow switched and all of Christianity is a big joke?
8. God is a businessman.
9. God wants attention.
10. He has nothing better to do.