The completely different industry structure. The film and theater industries work on time limited projects with a defined beginning, end and deliverable and most teams break up at the end of each project. Under those circumstances all a union can do to protect members is dualise, making lives better for insiders and harder for outsiders by restricting entry.

Long lasting organizations that have multiple overlapping projects with unions end up with compressed wage structures because the union campaigns for the median worker and the structure does not militate against that.