As some have said, it's possibly due to the "E 10+" rating they received from the ESRB. Guess those working at the ESRB supposedly believed Mythra's skirt was a bit too close for their comfort. Heck, Nintendo had to remove the Tharja trophy from Smash 3DS possibly due to the "E 10+" rating, as well as simmer down Bayonetta, an M-rated character who is known for her sexualization, to even get included as DLC. Sure, Smash Bros. has been rated "T for Teen" before, but maybe Nintendo and Sakurai's team decided on holding back to get a "E 10+" rating. Who knows, maybe the ESRB is a bit inconsistent, but I will lean towards that before going at Nintendo, especially since the rating does matter to them, regardless of what we think of the ESRB ratings.