I don't get it.
1. How is purposefully creating a gay NPC just for the sake of having a gay NPC supposed to be anything but offensive? I'm surprised gays don't see it that way as well. It's almost like saying y'all are so unimportant to the story that we have to go out of our way to work you into it.
Because all acts of writing the book are purposeful.
You don't just slip on the keyboard and create an NPC. They don't just materialize on the page. It's a deliberate act. As is making him married, which is another conscious decision. Martial status could be left vague, but saying "husband" has purpose and intent.
Homosexuality enters into the equation because most gaming material is still written by white men. The insitinct is just to use the male pronoun and describe people according your default. I write people like me: white cis males in heterosexual relationships. Any variance from that is deliberate, because I know the world isn't entirely people like me. I have to consciously vary from what I consider the norm.
That can be someone who is gay (unlike me) or extroverted (not like me) or racist (not like me) or Machiavellian (not like me) or dark skinned (not like me) of a colossal jury douche bag (hopefully not like me...).
Each is a conscious decision, so the world isn't populated by cyphers and author proxies.
2. Most heterosexual people dont play d&d for anything to do with sexual identity. If sexuality comes up it's typically background noise or because the group finds the fictional situation amusing. That's the disconnect we have with purposefully forcing sexuality or sexual identity into the story. Because of that many of us find the act of forcing anything like that into the game as offensive
"Most heterosexual people don't..." Statements like that aren't particularly useful. I don't think I'd comfortable saying anything that's effectively "90% of people don't..." or "90% of D&D gamer's don't..."
Sexual identity comes up in my games a fair amount. I try to have people of colour, different ethnicities, and sexual preference. Just because it's doesn't come up in your games, do not equate that with "the norm".
But this is irrelevant. The point of adding homosexuals to the game isn't for the straight people. It's for gay people. It's for the people like Jeremy Crawford and Wes Schneider who were young gay men reading game books and seeing someone like them in the game they loved. It was the sign they were accepted and welcome. It was a symbol of how everyone is welcome in gaming.