>>84913028I think it's because the first image that came up for Scarlet Witch at the time (it's on Wikipedia) is a version of the classic costume by Frank Cho, who tries to make it look sexier than it does with other artists.
The classic costume is just a bathing suit, tights and a cape (plus the tiara) so it can look whatever way the artist wants it to look, that's one of the advantages of a very simple costume.