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Cop-out rationalization: conventional wisdom holds that IT/CS folks should jump every 2-3 years or they're leaving money on the table -- and turnover rates reflect that. They're going in 2 years anyway, so get what you want out of them before they go. Most of them can't write fizzbuzz anyway, and it's easy to poach better talent by throwing money at them.
> Interestingly, and in my observation, the managers got more leeway than individual contributors in terms of evolving slowly
Managers run the system, so the system evolves to support them and their needs, like a more reasonable pace. Another way to look at it is if you've made it through the burnout phase then you're going to hang around longer, so it makes sense to hold on to proven performers who have much longer employment horizons.
Naturally it had the opposite effect of us dumping boxes of them in the trash.
When I was at Amazon, this was the feeling with some employees around me: The stack-ranking meant they were made to a rat-race every year.
I can't seem to recall who, but someone higher-up let it slip when quizzed about higher attrition rate (back in 2010s) that Amazon believed in evolution, and that that meant the slow would eventually give the way for the fast and new. Someone even quipped in an internal email-list that employees were about 8th most important resource to Amazon right after the 7th most important resource: The paper-clips.
Interestingly, and in my observation, the managers got more leeway than individual contributors in terms of evolving slowly. I've also seen rest and vest among managers, but rarely among the engineers. Strange power imbalances, if you ask me, existed and could be felt across every organization I worked for.