Maybe there's a Laffer Curve of programming. The 100% programmers are doing 0% per week due to lack of life altering kickback or equivalent, and the 0% programmers are doing 100% per week but deliver no value. Somewhere in between, the 50% programmers are the ones who are actually delivering the most value.

Your 20% puts you somewhere on the curve, perhaps to the right of the optimum, which might also explain the lack of life altering kickback. It's a feedback loop. Management wants workers at the top of the curve, not at the interchangeable edges.

It may very well be that the mediocre programmers, who feel lucky to be employed at all, are carrying the industry on their shoulders. Oddly enough this gibes with the widespread management attitude that they'd rather reward a mediocre person who works hard, than a brilliant worker who appears to be taking it easy.