Yeah it’s extremely sketchy but legal. Sports betting is treated as a game offered on the casino’s terms and they get to choose who and for how much they’ll play with. You can see it in the financials of the big companies. Where the theoretical win for the casino on most sports bets is around 5%, DraftKings and the others are regularly hitting 3x that much. They ban/limit winners and push everyone else toward bad bets (e.g. same game parlays).