Well, you raise a valid point: Heteronormativity is prevalent in so many African, Latin American, and Asian cultures, as well.

I suspect it's because America has been ruled under a Eurocentric culture for so long that people of European descent receive an outsized stigma of embracing heteronormativity. Orientationism and genderism from White people shouldn't be used as a pretense to excuse or rationalize such discriminatory behavior when it's exhibited by Black and Brown people.