Probably because GG audience expects them to be pure while BG fanbases enjoy them being sexy. Or rather be sexy in a way that only they’re comfortable with. Ofc this expectation of women is fueled by misogyny.
It’s also a double edged sword because people in places of power are usually men so the dynamics of GGs doing sexy choreo Vs BGs doing it is also different. For example the very same people who make threads like yours OP will turn around and say the CEO is manipulating the GGs or they’re forced (this can very well be true as well) This point is especially relevant for an industry like kpop which is so heavily controlled.
Anyway this sort of whataboutism doesn’t lead to anything more that purity culture. Someone will comment “well both shouldn’t do it” like as if that means anything with their whole chest lol.
In the end hwasa should be allowed to do what she wants but threads like yours asking why BGs don’t get criticized doesn’t lead to anything productive. I’d rather just argue that a grown woman should get to do what she wants.