People often don't act reasonably, and "should" isn't "will". That was part of my point. OP is looking for a reason, and sometimes there isn't a reason that could be supported logically.
You are absolutely right. I guess the point I was trying to make is that companies are not considerate when it comes to a candidate's time. IF after making a candidate go through a coding test or several interviews you still have doubts then don't hire him, simple as that. Nowadays companies/hiring managers/interviewers are used to treating us like crap, sometimes for their own amusement.Expecting candidates to pull out magic in a coding challenge is becoming more and more common, even when they know that a candidate won't be able to pull it off, it's almost as if interviewers enjoy turning people down and watching people struggle during interviews has become a (sadistic)leisure activity for them.