Have you ever graded tests for an entire class? I did so for two years when I was a PhD student and had to work as a TA. It does not matter if you are an expert in the subject because the problem has nothing to do with expertise, it has to do with how our brains work. The worst case is when most of the class answers the question correctly, and you don't encounter a mistake until you have finished grading most of the tests -- your brain really wants to just keep repeating the same motion (e.g. writing a check mark) and even if you spot the error you might accidentally mark it correct anyway.
Really though, this is missing the point. Yes, grading tests and homework is different from sorting mail, but both are tedious tasks that involve a lot of repetitive actions -- hard for the human brain, but easy for software. Software does not get tired or distracted by other responsibilities (or non-responsibilities). We have already been using software to grade tests for a long time now, but mostly for multiple choice questions; AI will expand the scope of that.