If you have 40 years of D&D campaigns where even a quarter of the characters are of any defined sexuality I'll... buy you a kitkat or something. (what, I'm poorUh huh. I'm sorry but do you have a point? Because I'm really not interested in throwing 40 years of D&D campaigns in your face. If you don't think that the vast bulk to the near totality of TTRPG material (and not just D&D) is straight, white and male, you're either not paying attention or playing dumb to pull a gotcha. And I'm not interested in either.

My point is that the majority being straight, white and male is a brush you're (/your DM's) labelling them with, not DnD.
NB: I'm not talking about things like story books or movies here, as they are a different beast from the game itself.