Are you... are you saying the skeletons are all male?
I dunno if you know this, but inside of all of us there's a skeleton RIGHT NOW!!! (AAAAHHHHHHHHH scary!) [joke]
I could see a ponytail as one of the cosmetic variation, as there is one with a beard, but ponytails aren't explicitly female anyway. Also neither is pink. There is a lower-body variant with a skirt, but guys can wear skirts, too (see: Harry Styles).
I think representation is great, but seeing all the skeletons as male I think is only due to inherent sexism. There's nothing "male" about the skeletons (except maybe the beard, but bearded ladies can be a thing, too). Most of the variants are pretty gender-neutral, although if you go toward more traditionally feminine colors there is the "sunken bones" variant for the skull. Otherwise it is mostly: wearing a barrel, being filled with a crab, having a bucket on your head, etc. All fairly gender-neutral things.