In the game industry (and in fact, in any professional industry), employee turnover is expensive. If someone leaves the company and you have to replace them, there's the expense of interviews (which take a lot of time away from senior people) and then the extra time it takes the new hire to get productive. Companies that realize this do what they can to retain their employees. Indefinitely.
Being a professor is different. In my case, "turnover" means that a student has graduated. It means I'm doing my job correctly. It also means fighting against the instinct of "gotta keep our best people around" that I'm used to from being in the industry.