Why exactly was Arkham knight rated M?

I didn't notice anything incredibly violent or noteworthy ad being too extreme for a T rating. The psychological stuff wasn't anything we hadn't seen before in an arkham game. There wasn't excessive blood or gore. The most extreme thing was Barbra shooting herself, even then there was not blood splatter whatsoever. Professor pig's most wanted was kind of disturbing, but again I think it'd be mostly intact with a T rating.