It doesn't, more efficient lines = better odds for punters. That is why Pinny/Asian books have better odds. The worst experience for gamblers is one with significant government intervention and/or limited professional involvement because there is no price discovery. Bookies don't just return that value to customers, in practice, they spend it on wildly expensive marketing, this means they have to offer lower payouts, and then spend inordinate amounts of time and money stopping professionals picking off their shitty lines.