Why did some European rulers reject Catholicism in the Protestant Reformation?
They wanted the church to have more structure, especially in the face of Muslim
invasions from the east.
It was common practice to change the state religion in Europe.
They hadn't been paying attention to what priests were doing before this, but
Luther's revelations shocked them and made them reform.
It gave them more control over their own kingdoms, since they could become
head of church in addition to already being the head of state.