They could if they wanted to. No one is stopping them.
Ballet is all about women, even the lead male is only there to hold, lift and twirl the prima ballerina. The tutus, the pointe shoes, they are stunning and breathtakingly graceful, all eyes are on them. Also women far out number male dancers in almost all classical productions. The whole corps deserved ballet will be only women in tutus with the only male dancers being the lead male, and some male characters who also dance pas de Deux.
For a male centric ballet to exist is highly unusual. So it's hardly like the women are being erased. The male swans are male because they are strong and powerful, a woman in a feathers breaches and a nude top would not have the same powerful presence the same way a male dance in a tutu and pointed shoes would never be able to do the sugar plum fairy.
Les Ballet Trocadero are all men who dance en pointe in tutus doing comedy versions of the classics. They are fantastic. They are so so talented, they are so elegant and graceful, yet it's funny because they are clearly a man in a tutu. Even dancers so talented could never portray the actual dying swan in swan lake because it's a feminine, delicate role they could never portray no matter how skilled they are. And it's the exact same reason a woman could never dance a Matthew Bourne male swan, she simply doesn't have the physical power and presence.
But that's ok, because it's art, and art has many different facets and is creative and entertaining and powerful in many ways. It would be dull if you took away it's many facets and told creative directors you can't do that because I don't like men dancing swans, swans are for women.