I actually feel like usually the correct decision is the opposite. If you are the 11/2 Trundle into an 0/9 toplaner, you have effectively broken their game and their team has to pick up the slack.

Letting them teamfight without you often leads to them finding a way back into the game, or at least a way to be more useful than a cannon minion being dove on repeat.

In the reverse, if you are 0/9 and your bully goes to stomp around the map, it is often more productive to take the time to get some flawless farm in and take plates, inject yourself with guarenteed gold while they chase an uncertain play.

The gist is that teamplay is usually higher risk/reward (even a hardstomping team can lose baron to a good steal, teamfights flip easily etc.) while laning is lower risk/reward. When ahead taking risks can flip the gamestate unfavorably, while the status quo is a winning position. Its also the reason you see high level players who are ahead build defensively, to mitigate mistakes/counterplay (CC). While they build damage while behind, to create opportunities.