>>15727403American cultural stigma against too much violence in women's wrestling. In American wrestling and storytelling tradition, fights between women are not serious and only consist of superficial violence. This is viewed as being sexy, at least traditionally speaking.
The fear is that if you bring over the Joshi level of violence and put it on TV some senator will call it violence porn or something like that. Japanese politicians on average are a lot less concerned with pretending they care about women than American ones are. Also, violence against women in entertainment is one of those rare bipartisan issues in the US, both parties are vehemently against it.
WWE is generally smart about it and lets the girls who know what they're doing do the big risky spots, but only on PLE. Putting it on TV risks pissing off some 80 year old senator or the FCC.