That way we could exercise our options as they vest, instead of holding out until an event to get some liquidity. It keeps people trapped.
There is more to the quality of a job and your life than having the highest total comp possible.
Having a lasting and enjoyable connection with your teammates is valuable too; you spend hours a day interacting with them, and teams of people you can really get along with are few and far between.
If jumping ship every 6 months maximizes your comp, but you never get the chance to create professional relationships as you jump from ship to ship, I'd say that's going to usually be a bad tradeoff.
There are other axis as well, such as a team with a reasonable manager who lets you spend time with your family, or a company that works in an area that aligns particularly well with your interests.
Treat your salary as your total income and equity as a lottery ticket?