When you negotiate a higher salary, you are saying to your boss, look, I know I am creating more value for you than I'm getting as a wage, and I know you can't just swap me out with somebody else. You're actually making a demand that needs to be underwritten with a credible threat, no matter how politely you communicate that. You demand that the company realign your wage with your value (actually, you demand that they get closer, they of course never pay you your full value, or they don't make any money).
It's really that simple. You get what you have the power to get. It's not magic, and it's not all about the attitude or w/e.
Of course we are all still constrained by material reality! If you can't make the credible threat, you can't "just" negotiate. (Duh)
Edit: obligatory "above is true in my experience, YMMV"
Hit Senior (easy to do after 5y) and game companies throw money at you to come over because getting people in who have a shipping mentality is hard- most people who want to be gamedevs see the glamour, those that ship see the pain a mile away and how to avoid it.
The issue might be that most who become senior do not really move because the tool chains are largely different between companies. Frostbite and Snowdrop are incredibly different game engines and even those working on Unreal/Unity at the AAA level invariably maintain a fork due to limitations in the engine itself which makes it not compelling to sacrifice all your knowledge.
Also, I find that most companies end up turning their C++ into a custom C++-like language with fancy types like growable hash tables and vectors. Many of which have quirks which require experience otherwise there can be footguns. (Some functions may be more correct but quadratic and others are fast but less precise and knowing when to use what is part of being a senior in some companies)
So yeah, of course all the guys leaving Blizzard are getting snatched up, and there is a lot of demand to fill their shoes, but those roles need to be filled by equally competent people, not just anyone off the street.
It seems that in games, you either have leverage to negotiate, or you don't. There doesn't seem to be a credible middle-ground like in other software disciplines where warm bodies capable of writing for loops are all that's required to build the product.
I've heard about game dev's surplus of workers for at least 10 years for almost identical reasons in most of this thread, and that would make nearly anyone a senior for sure, so that problem should have been "fixed" by now.
What I also see is people leaving due to crunch and burnout - companies which are famous for it seem to lose a large number of employees every time they finish a project, I see that in applications. They aren't being fired, they are just burnt out and they look for a place with better work life balance. We have a bit of a reputation for being really good about it so we see those people apply to us.
And then finally, the "I really wanted to work on X all my life" still applies regardless of seniority and if the opportunities appear people take them no matter the compensation.