This actually does hit on the major difficulty in unionizing, which is that people want to make games. It seems fun. It feels rewarding to point to something bringing joy to your friends and family and go "I helped make that!" Because this feeling is so common, it's extremely easy to find someone to to do the job for less. If you're a cost minded manager (instead of a results minded manager) you might be willing to take on 3 dirt cheap juniors to do the work of one really expensive senior dev.
Yes. Often (though not always) by increasing barriers to entry. Either directly, for example by requiring union membership, or indirectly, by increasing the cost of labor, which could mean that companies in the industry will higher fewer people in aggregate.
So yes, unions are one way to try to solve that problem. But if you choose to advocate for that, just be aware that attempting to solve these problems via a union would result in trading one set of problems for another: you'd probably end up with better working conditions, at a cost of new, artificial barriers to entry for all those people who want to work in that industry. Maybe it would be worth it, I don't know, but given the root causes, it definitely seems like this tradeoff would exist.