Why did the opponent resigned before I mated him?


After 25 moves facing your king and queen with just his king, it was probably apparent to him that you were in no hurry.
Did you know that a relatively simple technique could have mated your opponent quickly?
https://www.chess.com/lessons/winning-the-game/checkmate-with-the-queen
It should really take you no more than 10 moves from when you got your queen.

He knew it was hopeless for him and respectfully resigned instead of running your clock out and getting a draw (by timeout vs insufficient material)

Probably dinner was ready or some similar reason. That resignation just threw away a half point: there is no implication that black knew how to mate with a queen.

Probably dinner was ready or some similar reason. That resignation just threw away a half point: there is no implication that black knew how to mate with a queen.
Me? The opponent resigned after I declined their draw offer.
That's before checkmate!

Probably dinner was ready or some similar reason. That resignation just threw away a half point: there is no implication that black knew how to mate with a queen.
They resigned in move 75.