I suspect it goes hand in hand with the greater prevalence of stereotypical m/f romance genre plots and tropes

This might have something to do with the fact that most of the pro m/m i've seen is being marketed as Romances to a Romance audience.

I really do kind of wish you'd used the word "archetypal" rather than "stereotypical" there, because the Romance, like the Hero's Quest, contains certain specific elements for a reason, and it isn't because their readers or writers lack imagination. It's the old thing about the jelly beans and the chili recipe: jelly beans are great, and chili is great, and a chili recipe calling for jelly beans isn't a chili recipe...