Look at where Fanduel/Draftking/Caesars type sportsbooks make their most margin-- it is parlays. Probably 95% of people wagering on these sites don't have even a tenuous grasp on basic statistics, yet alone how to derive actual probabilities of their action for simple spread/moneyline/total wagers. When you're letting them combine 5 wagers each with an EV of 90 cents on the dollar, the books are loving it. Layer on that these books simply ban winning players, it is insanely predatory.

Prediction markets, as they currently stand, are at least better with regard to having a lower take and are less predatory in their wagering products and marketing (although these points can very easily change, but the complex wagering menus will be less liquid and harder to grow). If the house cut is 1-3%, that is still drastically better than the other parimutuel wagering in America, horse racing, which is typically 20-25%.

One structural difference seems to be incentive alignment. Sportsbooks monetize volume and friction, while prediction markets depend on sustained liquidity and accurate pricing, which is much harder to maintain at scale. It feels less like a failure of the idea and more a mismatch between economic incentives and market expectations.