they also replaced her love interest with a completely differen character who "hates her for the entire film until after he discovers she's female"
so they're basically doing it to erase the implication that her love interest is Bisexual (the character in the original movie falls in love with her while thinking she's a man, and doesn't fall out of love with her after finding out she's a woman, implying he's bi)
edit: the fact that Disney feels the need to retcon his existence also makes me worry that Disney never meant for him to come across as Bi....but as being a Gay character who was "cured of his Gayness" by "meeting the right girl", which would explain is initial rage when he found out she was a woman
(the romantic subtext definitely starts while Mulan is in drag, then He freaks out when he finds out she's a woman, then at the end he's just resigned to the fact that he's in love with her)