I think it's important to understand that there's a significant amount of selection bias possible here. In general, folks who switch jobs every two years are the folks who are not getting offered big raises by their current companies. The ones who are getting offered big raises may still choose to leave due to other reasons, but they often will choose to stay instead. And they won't be making a big fuss about it onli…
I mean, notionally, yeah. But that's putting the employer up a pedestal of competency that may not be justified. Less poetically: it's forgetting just how hard it can be to measure that value, and the role of optics and "managing up"; there's also the consideration for excellence on never-released projects; in such a case, do you or do you not deserve a raise?
There's many more factors that go into "your business value"; intelligence, passion, communication, and luck (right place, right time) are some, but not all, of the factors.
What you are saying is definitely correct in an ideal world, but we live in a sub-ideal world; that's why there's valuable problems to solve in the first place.