There is some culture elements in there even if the cynical reasons are the same - those other higher paying occupations are require working with people instead of their products. The dynamics change. Actors need to work with directors and any other actors in scenes. A union's arbitration there appeals as protection for the workers from each other. Workers would agree that they don't want to have to work with a guy who regulary assaults them for instance. A very reasonable case.

This structure like most tools also has a dark use. Not as a "is bad" but "not automatically good". It could be used to perpetuate discrimination as the members don't want those <slurs> working in <their occupation>. As common for bigotry it is not a good move for long term health.

Anyway the sociality seems to be an underemphasised factor to unions. This isn't to say that the non people-to-people jobs should never unionize just that it is especially artifical like say the practice of putting rubber duck covering a fence post point - it is harder to set up and maintain as norm when the first question everyone asks is "Why bother with the duck?"

As far as I am aware there are no serious scientest unions - doctors boards are the closest thing but there are many significant differences.