A good chunk of students don't care about learning.
I think it is only relevant when the score is way below the bar. Otherwise, who cares..A lot of people. Mid to high scores are commonly used for P&T and raises outside HRMs. Plus, many economists have teaching focused jobs and using a poor evaluation system doesn't benefit a soul.
There is also the off chance that a better evaluation system might lead to better teaching and thus more learning by our students...