Here's some more... looting, the temple or region, can take money from the temple. Also, looting the temple can cause part of the estate to become vacant/wilderness. Faiths would be forced to use gold to protect their assets.
Because religions just have so much gold they don't know what to do with it all, right?
However much I disagree with the stance, Tom has said that there wouldn't be a way for lords to automatically fund their temples. Giving temples an estate to get an income from would just be a different way of implementing the old tithe suggestions.