My understanding is that on-set crew and actors are hired by a temporary company set up for that movie specifically. When it's done, they're all out of a job and need to find a new temporary company to work for. This makes unionization of the individual temporary companies essentially impossible.
The same isn't true for folks who work directly for Marvel on an ongoing basis.
The people can't unionize a company that exists for less time than the average unionization campaign takes to form one.
This is why the writers and directors in Hollywood are able to unionize as an industry rather than per-company. (See, in contrast, the recent Starbucks unionizations; each individual location votes and creates their own union with a dozen or so members.)
> Sectoral bargaining was promoted by the National Industrial Recovery Act of 1933, but struck down and replaced by enterprise bargaining under the National Labor Relations Act of 1935. Today industries like screenwriting, hotels, and railroads still see sectoral bargaining predominate.
Actors and crew have things like the SAG that negotiate with the movie industry as a whole, because it's functionally impossible for them to unionize otherwise. If you're a unionized Starbucks worker, they don't negotiate with the coffee industry, they negotiate with management at your one particular Starbucks store, because that store is an ongoing permanent concern.
VFX artists employed by a permanently-existing organization like Marvel don't need this exception. (Ones employed by a transient production company for a single film would.)
Why are you acting like an industry wide union is some exceptional thing that can't happen?
There have been union vfx and animation studios in the past. The industry is broken up into many companies, which is why people talk about unionizing as a whole.
What is the actual point you are trying to make here?
The same isn't true for folks who work directly for Marvel on an ongoing basis.