But we absolutely see backlash of the type of “why does he have to be gay” in response to something as simple as two men holding hands, or other things that would never be seen as “making a point to mention someone’s sexuality” if that sexuality is straight. I’m generalizing away from this particular example and addressing the idea that anything that isn’t cishet is abnormal and requires justification.
They’re agreeing with you by saying that no one’s sexuality should be forced to be disclosed, much less should it require justification unless absolutely necessary.
This isn’t about forcing people to disclose their sexuality. “Why does he have to be gay?” Is almost always an effort to force people not to disclose their sexuality, but it’s only ever used when the sexuality being disclosed is non-straight. You have never seen and will never see any reaction at all to a straight cis male character simply using the phrase “my wife” but a cis female character doing exactly the same will elicit a backlash. They’ll dress it up as being against unnecessary sexualization, but the only sexualization that’s ever unnecessary is queer sexualization. Straight sexualization is never a problem.