Games depend on sales and they're extremely complex, so they take a very long time to build. You don't know if the game is going to sell well before you make it

Games depend on sales and they're extremely complex, so they take a very long time to build. You don't know if the game is going to sell well before you make it. They're just like movies in this respect; it's a "hits business", and only a few companies last very long under such arrangements. Additionally, people are desperate to be employed by a game company, so the competition for stable/permanent employment is fierce. Most software developers are employed to write custom software for internal use by their employer, which is expected to last for years and will generally receive a lot of continuing investment. Almost every company of substantial size has such a project, so there are plenty of stable employment opportunities. If the company doesn't want to use its old software anymore, they keep their employees onboard because they have useful knowledge about the business and what does/does not work from the prior package. None of this is really relevant or true of game companies.