Because in real life they associate it mostly with gross bodybuilders.
Most women don't have any incentive to be in the middle of conventionally attractive and buff. Though thankfully that's changing with Instafit girls who know the right mix and workouts that make everything just fantastic.
Also it helps comics are the only medium that can do something like OP easily. I mean most cartoons nowadays are comedy shit so they don't really make attractive buff women.
I mean Young Justice is getting a 3rd season still so that might have one or two like the first seasons.
Also video games.>>93860746
To be fair actually buff women is pretty rare in comics, most are just normal hot chicks.