There are robes -basically the same as dresses but the cut makes all the difference. And "no gender binary in space" is all nice and well but in writing, words still have certain connotations and "dress", especially based on Amidala-type designs, has the connotation of a certain kind of cut that would ridiculous on someone with Adam Driver's body type.

And basing an aesthetic on something does not mean "have to copy it exactly". That's just lazy.