I’ve been in several matches (few overall but still significant) where my team is clearly winning, with armies and bases in front of the opponent’s original treaty circle but masses of walls (looking at you Portuguese and Chinese) prevent us from getting a decisive victory via conquest. Or worse, masses of walls help hide vills that spiteful opponents send to every nook and cranny just to waste the victors’ time. It is a bother to hunt them all down, even with spies.
These stall tactics are punished in Supremacy, so Treaty could be the same.
Adding the Monopoly Victory option would facilitate ending matches that are, for all intents and purposes, decided and save everyone’s’ energy and time.
(Potential objection) It isn’t exploitable in Treaty because you can’t build most trading posts until after the treaty anyway.
(Potential objection) The match won’t end prematurely. Quick, decisive treaty matches happen all the time. Monopoly won’t affect that. If the team under monopoly pressure isn’t able to siege any of the mid map trading posts for 5 minutes, then they are probably going to lose regardless.