well, it sounds like they chose poorly then. A political campaign requires you to pay attention to politics; having the noble, who is necessarily the focus, be disinterested makes the whole politics thing not work. Was the player doing the noble truly interested?

It might also not be the style of play they (or some of them) truly enjoy; sandboxy style play requires a lot of proactive behavior, some people are muhc more reactive.

If you had to pressure him to do anything, then the concept wasn't working, and an OOC talk with the players was necessary to decide on an adjustment.