There is a sort of stagnancy that can surround people who have been there for years though.
For many devs, the first 3ish months you lack context to be super useful, then that first 2-4 years of hard work and enthusiasm are probably your peak productivity. It gets harder to maintain enthusiasm as the years go by, so some devs who are cruising with 5+ years might actually provide less long term value than a new hire.
The 5+ year workers understand, and have experienced, that the promotion system is designed to extract the most value from the greenest thumbs. Tenure is rarely rewarded. Why work harder and harder for nothing?
For many devs, the first 3ish months you lack context to be super useful, then that first 2-4 years of hard work and enthusiasm are probably your peak productivity. It gets harder to maintain enthusiasm as the years go by, so some devs who are cruising with 5+ years might actually provide less long term value than a new hire.