Much of the expense for 'talent' comes from the artificial scarcity created by marketing. It's a vicious (or virtuous, depending on which side you're on) circle: a company spends marketing money, which attracts theaters, which means big audiences for the movie, which means that newcomer with a minor role gets exposure, which increases their appeal as a lead actor, which means their next movie will make more money. There are only so many actors who can appear in a 'major' release because a) there are only so many screens and b) there are even fewer movies showing on those screens because the blockbusters dominate the limited number of screens. There are always more actors (and directors and screenwriters, etc) that have the capacity be 'stars' than the system can accommodate. That system is built primarily on marketing, not talent.