We don’t include stuff like subincision because where the frak does that happen and how often does it happen? All 4 types of FGM happen in Africa, Europe, Asia, North America, Australia and the Middle East; FGM (in all its forms) is usually performed on underage girls with razor blades, bits of glass, knives, etc in an unsanitary environment. This thread is about circumcision and not subincision because the latter is extremely rare and virtually non-existent in Western countries (adults choosing to have it done notwithstanding) hence irrelevant to Western legislators. The only widespread form of male ritual genital mutilation is circumcision (removal of the foreskin), which is not analogous to 3 out of the 4 forms of FGM. In fact, the least severe form of FGM (removal of the clitoral hood) is analogous to circumcision.
Do you really think that legal female circumcision would be done with razor blades and bits of glass in an unsanitary environment? You can't really get more underage than babies either.
I doubt legal female circumcision is going to include that whole stitching the labia together shit (not that the concept is really any nicer than cutting off foreskin anyway).