I think it's easy for us armchair quarterbacks to say "game = million". After 15, 20, 25, 30, 35 days it's probably very easy to lose sight of the million and drift. That's happened to quite a few contestants. Plus they only have ONE social group - the other players (or perhaps only their specific alliance). Add to that undernourishment, borderline starvation and dehydration, and a routine of doing something important every 3 days.
Holding the fort on old games that play the same as the new ones, minus the $400 price tag.