I don't think it's all religion though. FGM is not a thing in most of the Middle East, for example, whilst its a problem in many non-Muslim communities in sub-Saharan Africa.
None of the pro-FGM Islamic articles or fatwas I've read ever specify what exactly or how much of it is to be cut; it's always just "not too much" and a long screed about all the "benefits" and the hadith. It's basically permission to butcher girls, could you imagine them being this sloppy and unclear about male circumcision

"yeah, it's sunnah to cut the penis but not too much, yo".