It looks like you are already up a rook and a minor piece minus a doubled pawn or two. You've already won - putting your opponent down a queen is just further humiliation at this point. He was better off taking the checkmate!
But seriously, I'm sure it never even occurred to your opponent to sacrifice his queen. However, it looks like he had problems way before that, so it doesn't really matter. His understanding of fundamental chess needs a major boost on all fronts.
I've noticed that a lot of players at my level seem to refuse to want to give up their queen, even if it means losing to an instant checkmate. I've had at least two recent games that I won because my opponent didn't want to lose their queen.
This is the most recent example:
The smart move would have been Qd2, which would sacrifice a queen but keep the game going. Instead, they chose Bd2 which allowed me to play Qf2#.
I wonder if so many beginners and lower-rated players such as myself are just too afraid to lose their queen because they get it in their head that it's the most powerful piece, and they tend to think they can't win a game without it? Even if sacrificing their queen means taking their opponent's queen?