Some people seem to assume that mutually hostile cults simply end up murdering each other if they have an opportunity. That’s not really the case – between hostile cults, relations are strained, and the historic tension complicates peaceful dealings. There are difficult moments when hostile cults meet.
The Seven Mothers and Orlanth cults are mutually hostile. They can co-exist, but that co-existence is fraught with tension that sometimes spills over into violence. More often it involves the cults deliberately tuning the other out, refusing to interact with each other, segregating into separate communities, and that sort of thing.
In the cities of the Lunar Provinces, the Orlanth cult is discouraged by the ruling Seven Mothers cult, but that does not mean that there are bands of soldiers stopping the rural population from worshiping Orlanth. The Lunar Empire simply doesn’t possess the resources to do that.