Ask HN: What's the metagame of job hopping and raises

For myself - and a great many people I know - switching jobs has led, on average, to 40-50% pay raises. Performing well and getting promoted at a given company one rarely exceeds a low-single-digit adjustment.

Why does this phenomenon happen so consistently, across such a wide variety of organizations from tech startups, to non-profits, to massive corporations, etc.

Can someone describe the dynamics at the macro level that keep this as the steady state (would it even be considered a Nash Equilibrium)?