Perhaps anecdotal, but my opinion is this basically comes down to two general types of workers: those who know what competitive salary rates are and those who don't or don't care.
The first category knows exactly what they're worth and they'll push to get that worth. They know that if their current company won't pay that, they'll easily find another company that will. They end up switching jobs relatively frequently and get a raise each time.
On the flip side, you have the people that simply don't pursue higher salaries. They tend to get a job and stick with it for a long time. They'll take the 2 to 3% COL adjustments and an occasional promotions, but typically they'll stay with a company for years. While they certainly could find a better paying position, they won't. Perhaps because they like the lifestyle, the type of work, or even unaware that other companies are paying significantly better.