I'd theorize that this has something to do with the fact that the hippocampus is implicated in both determining locational context (for navigation) as well as task management and executive function. I've read a bunch of books on the topic of willpower that indicate that decision-making is a fairly expensive on a metabolic level, so this makes sense to me -- it's like you're minimizing the array of actions from which your hippocampus has to scan when it determines what to work on from locational context.