'Culture fit' -- the wild card that lets you reject any candidate.
I'm not sure that shows up in hours of interviews either...especially when most (all?) of that time is spent on "technical assessment"
And people who are getting better offers at better companies.
You'll never know.
I expect this to bite me as ageism in ten years, when a 23 y/o Stanford grad will be aghast that I don't spend my evenings playing with MeteorRails.js.