This has pretty much always been standard, and barring some sort of change in regulation, very likely always will be.
Horse racing has been pari-mutuel for a century, ever since the invention of the totalizator. The odds change as bets are placed, the bettors are betting against each other, and the house takes a cut. The track operator takes no financial risk. Sports betting, for some reason, usually doesn't work that way. Except, for some reason, golf and jai alai, which have pari-mutuel betting.
It's surprising that the online betting world didn't go pari-mutuel. Probably nobody would trust the service to compute the odds honestly.
Horse racing has been pari-mutuel for a century, ever since the invention of the totalizator. The odds change as bets are placed, the bettors are betting against each other, and the house takes a cut. The track operator takes no financial risk. Sports betting, for some reason, usually doesn't work that way. Except, for some reason, golf and jai alai, which have pari-mutuel betting.
It's surprising that the online betting world didn't go pari-mutuel. Probably nobody would trust the service to compute the odds honestly.