It's a good point, and one I expect most people have heard quite a few times. However, interviewees probably either don't have a job or aren't doing well with the one they have. As such, I suspect you're likely to get a larger % of the mediocre than you might see elsewhere in the industry.
I don't know how to estimate this skew, but it's probably substantial, particularly in this industry.
I'm fairly introverted and a competent developer; I've only done two interviews in my 13-year-so-far professional career writing code.
The first was for my first job after college. I only called one company in the city where I planned to move; they seemed good, so I got a job there.
The only reason for the second interview -- last year -- was because I moved to Europe, and decided after 4 years that working on the projects & jobs I could get from my contacts in the US wasn't great, so I'd have to (ugh) meet some new people.
I suspect there are plenty of competent developers who have experiences like mine. We'd rather go work with people we already know, the folks on the hiring side would rather grab someone proven, vs. (on both sides) interviewing with strangers and hoping for the best.
