I don't even think it's as clever as testing for anxiety. I think they have to be there watching your back to make sure you're not cheating - the problems they

I don't even think it's as clever as testing for anxiety. I think they have to be there watching your back to make sure you're not cheating - the problems they give are easily searchable online. As a by product they will also test for candidates who are super good under stress (or drilled Leetcode so hard there's no reason to be in stress).