Because he can, you have this logic because of planet earth and mostly religion stuff.
But if you go into another universe, where god interact with the world and won't care about killing and stuff, the world would be totally different from ours. Especially if there is superpowers and magic involved.
Do you think earth would be a paradise if tomorrow, everyone wakes up with powers big enough to destroy cities?
I will tell you what happens, in a month there would be no planet earth anymore
