They don't care about selling their food. They don't even want to put in effort once a month. They want to be able to tell their region, "Sell all the food over 200 bushels in the granary for 20 gold per hundred" once, then leave it forever.
Future trades could take care of that similarly to auto-trade. "Put 100 bushels on the market every week" and be done with it for a long time, unless something happens to your region to make your average surplus change significantly. I just wish "a long time" would be more than once a month.
