I think there is an expectation that it should not matter, and there is a reality that it does matter, and there is lots of discussion because the expectations and the reality do not match.
Why is there an expectation that it should not matter? Is it just childrens shows? In many countries you have to put a headshot on your resume, that seems very overt that attractiveness / looks does matter. In the west there is a large idealism over practicality sometimes.
Because we figured out that grading and selecting based on merit is better for society than grading based on subjective biases. I don't know what you mean by "practicality" here.