Ask HN: Is joining a new company every 2 years to increase ones salary workable?

It seems conventional wisdom is to jump ship every few years or so to increase one’s salary. But how is this sustainable? Why do companies focus on paying new hires more than paying their own, existing bootstrapped, and productive employees? Doesn’t this churn hurt engineering teams and lead to brain drains? Is this a myth and doing so is not actually the best way to increase one’s salary?