Unions work by helping employees get leverage so they can actually negotiate working conditions with the company. Any individual developer is easily replaced, but the whole workforce is not.

The current state of employee "choice" between companies all colluding to offer the same conditions is no choice at all.

How can they all collude, when entry into the industry is so easy? It's hard to keep big conspiracies alive. You can literally form a new game company in your bed room right now, and any people do.

Someone could break rank, hire programmers for a dollar more or an hour less crunch time, and still make a killing, wouldn't they?

No, they couldn't. There are a handful of companies making almost all traditional games, a handful more of indie successes, and then a terrible morass of companies making gambling traps called "mobile games".

If you're not working for EA, Activision-Blizzard, Ubisoft, Sony, Microsoft, Bethesda, Valve, Bungie, Epic, Rockstar, or Riot Games, you are almost certainly not working on a major video game project, and certainly not on a game that will make hundreds of millions of dollars in profit.

And conversely, if all of the developers on, say, World of Warcraft were to strike tomorrow, Blizzard would not be able to afford to replace them. That's the power of a union.

I have no idea where you got this idea that it's easy to start a gaming company. Unless you plan on making a mobile game, they're a very hard industry to enter, like all other art industries.