Getting into a movie industry union is very difficult and rather expensive to boot. You don't just get into these unions by showing up at the door.
The correlation to software would be having a list of progressively difficult things you have to do, so that, ultimately, only 10% of people make it in. The rest pay their dues by working minimum wage jobs and unpaid internships.
Unions, professional societies, licensing bodies, etc., all function primarily to shore up the in group. These groups then live off of annual license fees, dues, and other types of lechery. This group grows more and more detached, sitting in an office worrying about the meta-scale instead of actually doing any real work. Eventually the union and licensing bosses consume massive quantities of the otherwise-productive value just for sitting there in the middle. By this point, their approval has been codified into major corporate contracts if not literally made legally prerequisite. Good luck extracting them at that point. Right-to-work at least keeps that apparatus somewhat in check.
I knew a young woman aspiring to become a professional actor. She had spent years trying to earn her way into SAG, and had years left to go before she realistically had a shot of actually getting in. Unions are not charities. They exist to serve themselves and the people they decide to like, and no one else.
The fact is that all unions start with some exclusions. This would have to be a critical piece of any unionization as employers would have no incentive to agree to the terms laid out.
You're not really going to get rich from any acting roles.
Even at the 99th percentile, most actors don't make a ton of money, and the employment is both sporadic and punitively taxed. So those who are rich are generally those who were independently wealthy to begin with.
For every actor you read about who's making multimillion dollar contracts year after year for franchise movies, there are literally thousands who are making a modest living at best, or barely scraping by at worst.
I sometimes point out that every movie star they've ever heard of is a member of a union.
I think part of the problem comes from the decline in unions in the US over the last few decades. New industries aren't unionizing, and older unions are being undermined where possible.