I think the number one cause of the lack of hostile religions is that characters have no interests in joining hostile religions to begin with.
I think nobles in BM don't car about religion, because of the added authority over you an the lack of benefit but presence of penalty (religion does something bad, you can look bad because of it and the major one of gold. You need to give gold to expand and maintain but expanding your religion really gives no benefit to any but those on top because they look god for making a large religion. It's like a ruler and dukes trying to get more nobles but they don't tax any of their peasants so no one gets anything but they still need to pay for troops and pay to maintain their regions. Sure they have have an interesting role play in the start but since they don't have much nobles, the ruler and dukes aren't even that active either. That is how religion currently is done, IMO.
