If I am unhappy with how Google/big-N tech company works, there are other options. If I feel exploited, I can start my own consultancy and consult with just a couple of clients. I can start a startup and raise money quite easily in this VC market. I can built small POCs for a few customers within a few months and scale up from there. I can switch companies and go to a competitor. Hell, switching is almost always the more lucrative option.
I do not need a huge amount of money to enter or move around in the market, and even if I do, it is readily available. That's a 'free-ish' market.
Getting funding for an unmade indie game is substantially harder. The first demo takes years instead of months. The employee has zero leverage, because their access to the market is artificially limited through only a few hyper competitive AAA channels. There are many such broken markets, gaming is just an extreme case of it in our tech world. SpaceX worked in almost exactly the same manner. The free market doesn't work, because the market is not free.
In such a non-free market, the one who controls the supply (AA dev) can easily set up an almost ponzi scheme-esque revolving door of hyper exploitative setups. (modern academia with post-doctoral adjunct revolving doors is a similar example). The AAA studio is taking advantage of information asymmetry, and massively profiting from this use-n-throw setup.
Unions are a way for the demand side to combat the latent asymmetry of information and power in the non-free market. AAA studios make big promises to starry eyed new-grads who have served their purpose by the time they realize they were lied to and are disillusioned. (ie. Contract workers don't get made permanent. Crunch, hire-n-fire, lack of upwards mobility in the structure are endemic and permanent afflictions in the industry)
Unions can force companies to enforce the promises they make. No more than x% crunch. No un/under-paid interns. Path from contract-> fulltime. Some level of ethical standard for exploitation of school children using gambling techniques. Profit sharing ?
If the union's demands are too unreasonable or not reflective of their leverage in the industry, they will get left to die. (see the political unions at Google) If this was truly an information asymmetry situation, where game devs were paid lower than they were worth, then the union will flourish and sustain itself in the interest of the employees.
The realities of the unfree-market do not change, but the union makes sure that demand side (people who want jobs) can negotiate in a manner that actually reflects the cards they hold.
My opposition to unions in general comes from my general opposition to unnecessary bureaucracy. Bureaucracy should be avoided in don't fix what's not broken situations. Big Tech's free market looks healthy. Don't need unions. Gaming does not. Maybe Unions will help. Simple as that.