By comparison, replacing an actor is much more of a headache, and requires writing out or recasting a character. In some circumstances this could potentially ruin the show. That gives actors much better leverage for salary negotiation, particularly once the show has become established.
For example:
-An actor has to maintain a physical appearance
-at higher risk of losing income due to an accident since it could change their appearance
-has to travel and generally do more physically strenuous tasks
I am not saying actors should be getting paid more either. But prices are best determined by supply and demand curves, not by people’s “feelings” on fair and unfair.