@zeck123 Because the crossdressing tag only cares about the clothes not the character cosplayed. So a guy cosplaying Astolfo will be tagged as m:Crossdressing (unless they take the wig-only BS to the point of just being nude) and a girl cosplaying as Subaru Konoe is likely to be tagged as f:Crossdressing
To search crossplay more effectively within the Cosplay category you could instead use Gender Morph, because within the Cosplay category cosplayers are treated as if they are the character (or a genderbend version of them in that case) instead of merely cosplaying them. Gender Change, while also valid on those cases, is less reliable as because it can also be used to indicate the cosplayer is post-transition trans or using photoshop or a boobshirt (or similar) to look that way.