Here is how it goes: You are playing a game, your opponent is playing of normal enough strength playing reasonable moves. Things are even or close to for a while... At some point in the game you do one of the following things:
1) Gain some sort of material
2) Gain a long-term permanent strategic advantage
3) Start breaking through the defenses
4) Any sort of move after which a computer would say you are either winning or solid advantage
There is still a bit of material on. It's not over yet. With solid defense, your opponent could maybe last another 30-40 moves before mate, but it's eventually probably gonna be there unless you make a horrible blunder or they somehow pull a miracle save.
It's at this point they shift into a mode similar to give away chess. Here take this piece, and that piece, and this other piece go ahead and mate me easy. They are playing a sort of help chess where they try to lose faster...
If your objective has become "Just lose as fast as you can" why continue to mate and not resign?