It's simply selection bias. Anyone can write up a resume and land an interview. Most great people have jobs and aren't interviewing, so the talent pool of 'active interviewees' is limited to those who either couldn't land jobs elsewhere or are new. It's rare, but sometimes someone takes time off.

The quality of folks coming from a very selective program in a different country, however, has selection bias in the opposite direction; nearly everyone from there is going to be better, on average, than the 'average' interviewer, because as mentioned elsewhere, roughly half (likely a bit more) of people we interviewed could not pass FizzBuzz, despite having stellar resumes.

We saw the same thing with MEET, which I helped teach a decade ago too.