It can get very demoralising as an interviewer when you interview dozens of candidates, and none meet the bar - and even the ones you rate hire or leaning hire get rejected by the hiring committee. When I first started interviewing (at Google) I was like the Apple interviewers you admire, but I have slowly become inured the process and now I probably give candidates the impression that I've seen it all before and I would rather be doing something else - because it's true.

But the alternative is more filtering before the main round of interviews, to increase the base success rate of candidates, which many people hate (see many other comment threads on this post). And too much would turn off the best candidates probably more than the worse candidates, as they have more outside options.