Well my brother worked construction in the northeast where it is unionized, and it was an absolute nightmare for a variety of reasons. He was unable to work without a union card, getting that union card was very difficult without knowing someone because union jobs are highly coveted and thus kept artificially scarce, and once a member of the union he was forced to work with many lazy workers hiding behind the job protections afforded by the union.

What's to stop the same thing repeating itself in a game developers union?

I also worked for a construction union in the northeast, and our employer sent the worst employee's pay check to the job site via same-day courier to ensure that, once duly compensated, he could be immediately dismissed. The rest of the crew was thrilled to see him go. Construction is dangerous work, and none of us wanted him around.

At the same job, another employee, young apprentice, was found napping. He popped awake and was apologetic. Partied too hard the night before. The foreman sent him on a coffee run to get his head together. He wasn't fired, presumably because the foreman never reported him, and (at least for the rest of that job) it never happened again. Almost 20 years later, he still probably gets shit for it.

Bad employees can coast by in any job, especially hourly ones where the upper management is rarely onsite with the workforce. First dude got fired in short order despite the job protections. Second dude didn't, but (to my knowledge) not because of any union regs.

Anyway, I digress. There is, of course, nothing preventing some union horror story from taking place. There is also nothing preventing even worse labor exploitation from taking place (and we're already at 80+ hour weeks in some cases).

The biggest difference, though, is the labor market itself. The laborers in construction unions are temporary hires for a specific job. At the same time, most construction unions are craft unions with apprenticeships, where each new employee represents a risk/investment to training that person for many years. Nepotism abounds, because if you train a new hire for, say, two years, then they wash out of the program or leave to study engineering, they could have spent that time and energy training someone else.

By contrast, I would expect most gaming unions to look more like a public employees' union. It would represent permanent employees of a company, likely salaried. Not much would change in the hiring process outside contact negotiation. You get the job? Congrats, you can join the union.

The same thing that stops it from happening in Hollywood. Even the best actors and directors choose to join SAG and the DGA even though they don't need to.