Actors are the ones looking for a gig, often any gig, but when they have a choice, the highest paying gig. And believe me, every actor and writer in Hollywood wishes studios would invest more in mid-budget B movie not based on any cinematic universe: those are what paid many people’s bills.
As Union members, actors have a contract with studios that they negotiate every 3 years. Every three years since the last strike in 1960 they’ve reached a deal (and the result of that strike was the creation of revenue sharing for cable and film tv with actors and writers, which they are now hoping to apply to streaming).
No deal? Fine, studios have the right not to sign. But actors have the right to withhold their work. Eventually a deal will be reached.