I wonder if those people you're talking about just froze in the interview process, like others in this thread have mentioned doing?
Presumably it's possible to distinguish people who interview badly from people who lie on their résumé. The question is "How?" Followed by "How many interviewers know how to do this?"
The interviewers in these loops are generally quite introverted themselves, I know I certainly am. I believe we are sensitive to people who are the same and cut them slack.
My goal when interviewing someone is to determine if they will, on net, add more lift or more drag. If someone is so nervous that they can't communicate, they (sadly) will almost certainly not be able to demonstrate this.
Luckily, there are personal referrals. A strong engineer who interviews very poorly but has good first hand references will be given MUCH more slack.
Presumably it's possible to distinguish people who interview badly from people who lie on their résumé. The question is "How?" Followed by "How many interviewers know how to do this?"