Listen pork chop, you fat bastard, I understand how horseracing works. If you knew how to read, the question was "why"?

Horse racing also takes a percentage off the top and distributes the rest of the pool among winning wagers. That is exactly what moneyline wagers do. The difference is moneyline sportsbets are calculated at the time of the wager, rather than includuing the money AFTER the wager. The question remains, why the difference?