The why not is in my post.
So you're saying that all LGBTQ+ characters in modern media have to be original characters and established LGBTQ+ characters like Hercules, Loki, and Dorian Gray are off-limits because the writer is mooching off their popularity?
I disagree. I think you are moving the goalposts because, as you stated previously, you believe that nowadays including LGBTQ+ characters at all is a shoehorned political statement. In most cases it is and that offends LGBTQ+ viewers too. However, that doesn't apply to our current argument because it concerns the writing of a hypothetical story.
Once upon a time, I would have agreed with you. If a writer wanted to make Hercules Bi, I wouldn't care.
But it's all politicized and "woke" now. Whenever I hear about a "progressive" character, I roll my eyes. It means bad writing, cliched progressive buzzwords, and a pandering attitude towards minority characters.
Good stories told well transcend all this shoehorned progressive horseshit.
Japan doesn't have LGBTQ+ rights, yet their media includes whole genres predicated on unrealistically fetishing LGBTQ+ characters for the enjoyment of straight cis consumers. Boy's love, girl's love, traps, futanari, the list goes on.
You are claiming that politics has ruined LGBTQ+ storylines forever, despite the fact that there are currently countless novels and fanfiction which feature amazing characterization of LGBTQ+ characters. Based entirely on your political statements, I suspect you have been poisoned against the idea by the press. But I could easily be wrong. Are there any LGBTQ+ characters in fiction that don't offend you, that you actively enjoy reading their adventures?