Singleplayer Vs. Multiplayer AI

So, when I play singleplayer against AI, I often win after destroying all of the AI's Town Centers, where they request to resign, and I accept it. However, I was playing with a friend today and we did a multiplayer map. We destroyed the opponent's Town Centers, but they did not ask to resign. Is there a reason why that does not happen? Also, is there any kind of mod or anything that the community knows about to make this possible by any chance?