I've noticed that as well - usually done as a 'progressive' twist, although it usually does little beyond adding an annoying love triangle to the story.
I think that's the thrill of "last minute gays," really. Writers get the rush of "Ah ha! You THOUGHT they were straight, but they were really GAY all along! Aren't I the cleverest?"
90% of the time I hear about gaybaiting, it's usually in shows or series that most people wouldn't assume would be gay if they just watched the show. Who really expected Sherlock and John to be lovers? Keith and Lance? Finn and Poe? I don't care what fanart the showrunners liked and retweeted on Twitter; no one was gaybaited.