1. Are happy in their current title, company, responsibilities, etc.
2. Don't want to get a big raise
3. Just want to "do their job and go home"
I'm thinking of exactly two. There may be one or two I'm forgetting. Coincidentally they were also two of the least skilled developers I've worked with, I think in part because they had very little interest in growing professionally.
There are plenty of important, fulfilling, well-compensated careers in which you don't need to grow, learn, and expand. Software development is not one of them.