Because if you're so sure, then it's a profit opportunity for you. Talk is cheap, but you'll discover just how sure you are by whether you're willing to take the action of betting on your belief. And furthermore, seeing those bets will serve as incentive for those who know something to bet one way or the other, creating a price signal, giving us information about what's likely to happen, thus helping curate market expectations.

And if they're only betting bitcents then obviously it's not a very strong conviction.