Except for the steady ascent of salaries, there's been hardly any change over the last decade or two in the way teams pay their athletes. New CBAs and shifting market conditions have created wrinkles here and there—opt-outs, performance bonuses, franchise tags and the related holdouts—but the basic formula persists. Teams pay players modestly when they're drafted and in the few years after that. Windfalls don't come until a talented player reaches free agency or, preemptively, receives a contract extension or an arbitration deal.
This model has been sustained because it has made the very best players very rich.