Based off this from Tropes:

“So far as we can tell, both teams are all female, despite the fact that the games are supposed to be unisex. We even see some of the guys at Crystal Prep in training for the games in one of the shorts, yet both teams are comprised solely of female students. One has to wonder if the guys do anything of value in this school or Crystal Prep at all, as three movies have passed with Flash Sentry being the only guy to do anything even halfway meaningful back in the first movie but even then it was the result of plot demanding he do so, and done in a very half-assed way intended solely to continue to promote his status as Pony Twilight’s love interest.”