One hypothesis I don't see mentioned is that time limited roles pay more. For example, a person brought into to oversee an acquisition or transition is going to be paid phenomenally well (and, I think, rightly so). But part of that job is making your own position redundant. If you're still there after a few years, you aren't doing your job. I expect there are many other examples, roles that are project based and become redundant when the project is completed. And, I expect, many of these pay more than operational jobs, taking care of some day to day tasks of the business. Probably rightly so; if the projects successful, I would think building something new would create more value as it should produce something that continues producing value into the future - higher risk, higher reward.