Because the stupider the prediction is that somebody is making, the harder it is to get them to put their money where their mouth is. The Bayesian is hoping that $50 is a price the other guy is willing to pay to signal his affiliation with the other non-Bayesians.
http://xkcd.com/1132/
Is this a fair representation of frequentists versus bayesians? I feel like every time the topic comes up, 'Bayesian statistics' is an applause light for me, and I'm not sure why I'm supposed to be applauding.