The key difference between sports and other industries is that competition is the product that leagues sell. If teams could purchase victories or if the Vegas odds always favored the same teams, then the value of that competition would decline. In other words, New York Yankees tickets would not be nearly as valuable if they played against Little League teams. (Although the first game would be entertaining.)
For this reason, leagues argue that they must sustain some degree of parity between their teams, and they claim to accomplish this through revenue sharing, entry-level player drafts, and, most of all, salary caps — limits on the amount of money teams can spend on players.