You can sell your bet at any time, though. So if you put $100 on NO while it's at 3¢ and then sell them next week at 4¢, you're getting $133 back. You're not necessarily betting on the outcome, but on the sentiment over time.
That's true, but then the people you're selling to have to want to buy the shares. And if you're buying YES at 97%, you're not going to be able to sell the YES shares to anyone at much higher - because eventually someone has to hold it to the end.
It's true that this isn't as true for NO, because a small change can give a huge return, but that's asymmetrical. So there's incentive for traders to buy NO, hoping that it moves down, but not an incentive for traders to buy YES, since it doesn't have any room to go up.
