The difference is, electricians, carpenters, publicists, and company managers have no involvement in the creation of the production from an artistic standpoint. That's the argument here: that actors used to develop a play or musical in workshops or labs have some claim as creators of the final artistic work. Aspects of shows have been reconceived due to specific performers in development. The ur-example of performers having claim to creator is A Chorus Line, which was adapted from the life stories of its original cast. Performers have a lot of artistic input which effects how the show develops. In some cases, an original performance becomes the design for the role entirely, and future replacements model it.
I'm not sure if musical directors or orchestrators get a cut of the profits for their work, but the argument would be similar for them. But for a accompanist hired to do a workshop and has no artistic input? Not so much.
"...everyone finally shut up, and the audience could enjoy the beginning of the Anatevka Pogram in peace."