I suspect they intentionally regularly interrogate people who they know are innocent to train what a normal false positive acts like. that helps detect the true positives in contrast while training on true positives is difficult as they are quite rare. the interrogation strategy is just to impose a high level of stress on someone. i suspect a false positive will act very confused in contrast to someone who wants to hide something.
(with positive I refer to someone who is considered dangerous or an enemy)
having said that I went twice to Israel from Germany and coming back from Istanbul and never had issues. actually I find it quite exciting to experience the perfectly orchestrated security measures. obviously though also because I never got the tough treatment so far.