It's rather because the junior and the company disagree on how skilled the junior should be rated as they grow. At a new company, you get the benefit of fresh p

It's rather because the junior and the company disagree on how skilled the junior should be rated as they grow. At a new company, you get the benefit of fresh perception plus the honeymoon period to finish maturing. Static job slots are also a problem, though. It would be wonderful to see companies hire for a vector/trajectory at the company, but that comes with its own issues if the employee doesn't change as well as hoped.