Nothing, as far as I'm concerned. Unfortunately the regulatory landscape disagrees.

How betting on the performance of a company is any different from betting on the performance of an athlete or a horse just boggles my mind. Sure, in the short term the variance is lower, but it's still a fucking gamble. It's also the only legal way to gamble in all 50 states.

Wrong? Nothing. It just tends to attract the attention of regulators when done at scale. Even Nevada doesn't allow casinos to run proposition bets on anything but sports.