How Do You Know a Developer Is Doing a Good Job?

That sounds like an assertion that needs to be justified. Why is that the ideal?

100 products, 100 lines of code!

If you paid your developers per line of code, you would reward the inefficient developers.

https://en.wikipedia.org/wiki/Loop_unrolling

An analogy to this is writing essays, novels, blog posts, etc. Would you judge a writer solely on the number of words written? Probably not.

That's exactly how a lot of professional writers are paid.