In my experience(again, I'm sure it doesn't apply everywhere) - a lot of people
think they want to do games, but actually leave and do something else after a year or two - not enough to get to senior level, so not at the level when they can actually start seeing decent salaries and have that leverage I mentioned. So they are easily poached by software development/consultancy firms with better money. Then people who do stick around and advance to senior actually show very high level of loyalty, I work surrounded by people with 15-20 years of experience at the same company, they aren't interested in going anywhere,
mostly because they still enjoy what they do and after that much time the money is usually more than decent so....why would you leave. But obviously people still do, and again, I see people leaving after 20 years making games to "try something else" and they actually leave the games industry entirely when that happens.
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.