Probably because you have, at best, a few hours in an interview to determine whether or not someone can solve the hard problems. Many hard problems take more th

Probably because you have, at best, a few hours in an interview to determine whether or not someone can solve the hard problems. Many hard problems take more than a few hours to solve, so the interview process serves as a gauge of how likely a candidate can do this on the job; of course after other vetting methods were applied.