It is a lot easier to vet someone you have worked with extensively, or if someone you trust gives a recommendation. It isn't like there is some secret society -- it is simply the way the world works.

Those are extra bits of information that go into the equation and they happen to count for a lot. I don't really see a problem with it.

Why wouldn't they give extra weight to those bits of information?

Also, this happens all of the time with positions across the board in startups/companies. If I am a senior engineer somewhere, and we are hiring and the company thinks I have good judgement... of course they are going to take my recommendations of candidates more seriously than someone off the street.