because the average judge/jury/CEO/consumer/manager has no idea how to write code.
They can understand how a toilet is cleaned, how a sale is made, how a 1099 is filled out, how a fire drill works, how a sandwich is put together, how oil is changed, etc... but Coding might as well be a dark art.
Developers are part of a very narrow segment which has no reliable
Key Performance Indicators.
Part of that is developers are smart enough to game any system, because they can think in algorithms.
Want to track productivity on Lines of code? Fine, Developers can do NO WORK, and produce TONS of code
Want to track productivity on Number of defects introduced? Fine, doing NO WORK is the baseline for perfect.
Want to track productivity on Number of defects fixed? Fine, through the magic of hand wavery, defects can be found and fixed with no actual work happening
Compare that to well-defined Key Performance Indicators for sales... Bring in X dollars of sales, your performance is X.
CEOs HATE things they cannot measure... which means CEOs are a natural enemy of Developers.