I'm not sure I understand either, but the empirical evidence is that I get a very low volume of replies but almost every one is from someone very well-qualified

I'm not sure I understand either, but the empirical evidence is that I get a very low volume of replies but almost every one is from someone very well-qualified and worth interviewing. Like some of the other commenters, I think it is simply the quality of this community as a hacker-friendly environment (a testament to good work by pg and its members to keep it that way of course).