The only long-term career/financial benefit to staying anywhere ever is experience building/shipping stuff, and goodwill from people who might be positive references down the line. Beyond that, staying anywhere for too long is just leaving money on the table.

Employers of course have the power to change this. Any individual employer even, it's not a Nash equilibrium. If they wanted to, they would. They don't because they don't care. You don't owe your employer any more respect than they show you, which is generally close to "none".