There is no one reason why philosopher try to prove or disprove religion. In light of this let me make one important observation.
From time immemorial, people have talked about religion. There have been debates, controversies, and the like. Part of the reason for this is because in the end no one can prove or disprove religion. Think about it. How can you prove or disprove God?
Religion is a matter of faith. This fact alone makes religions debatable. Hence, there are people who try to prove or disprove religion. I suspect that this will continue as long as people are around.