Because they both look shit.Johnnyallstar said:
The problem is not the costume design itself, it's how it's translated to screen. Daredevil, Spider-man and Iron Man (Think about it) all worked while being very close to the source material. ironically the X-men movie costumes look more dated because they have no personality and came out when black leather was the vogue for cool. I don't think for a second they should have gone with the old designs but the new movie looks pretty good with the yellow.
I think the costume was designed for the wank happy crowd.(males 14-35) There are loads of other ways a Wonder Woman costume could have looked good. (On a different actress is one)