I'm sure licensed themes benefit all involved. The theme owner gets licensing fees and advertising along with a say in how the theme is presented (for good and bad).

The manufacturer saved a lot of time and uncertainty involved with creating a theme. They will typically have a lot better idea of the appeal of a licensed theme (based on franchise popularity, sequel performance, etc) than with original art/theme.

Of course ops and players love them because of the instant association that adds considerably to the "attract" mode and coin drops.

I don't know if there's been a look at quantities of licensed machines produced vs unlicensed. But looking at the system 80B theme-knock-off games, they seemed to produce quantities similar to system 80 and better than system 80a licensed themes. So maybe its only necessary to be close to a licensed theme to sell. I wonder if a pin company could even get away with those sort of knock-offs today. Perhaps mix licenses up to help keep the lawyers busy - Unobtainium Man, Indianapolis Jones, Attack from Mordor, Wizard of Ozzie