Think of it the other way.
Bitcoin people are unhealthy and is always in front of the computer right?
So, forget bout incentive and think about health. 
You are right but I think a lot of people think more about "money" than "health". So if there isn't an incentive no one (or only a little group of person) will play for gain some of "health".
PS: fantastic phrase 'he was able to generate
5 cents in equivalent bitcoin payments.'
