I think it's because Mario series have o lot of that magical things, and it's not serious like The legend of Zelda series, so Peach is that "fairy tail princess". When Daisy was created, she was made unlkike Peach, and how that sports series already existed, I think they decided to make Daisy more like a tomboy. And I don't think Rosalina is this happy girl, I think she's a more serious queen.
This is just what I think, I don't know if it's really this, but that's my opinion. I hope I'd helped :)
she is so girly because now really would a tom boy be captured by bowser wating for a prince or someone to save her? no se would beat bowser herself but now really peach is not so girly after all she went on an adventure to save mario on vibe island where she fought enemies and bosses so is that soooo girly?