I do that same in the MP i ask workers can they do this or that depending on what i want and only to hire them and they have no idea, and when you are TRYING to help them so they do know they ignore me, so i think they really do know but choose to not to do as asked of them deliberately, i'm not saying that every single one of them do it but i bet there is quiet a number of them who do.... as for giving instructions in the MP i find this bit hard at times as there is a large number of workers spamming the screen and trying to find someone to Private message can be difficult with the constant flooding.
If my workers want to chat i will chat if they don't that is fine, a simple 'thank you" when they have finished only the polite thing to do...
Happy farming may your crops and prosper