[ylg]

I'd say the fundamental issue is that they are solving the Yellow Pages problem, i.e. "how do I find a list of people who say they do what I need" or "… need what I do". That's not been a valuable problem to solve since, well, the Yellow Pages.

A valuable, related problem to solve is "how do I find a few people I could rationally believe will help me get positive return on my investment." And, so far as I know, no one has figured out how to convey the information we humans need to arrive at that belief or trust via web pages (or printed yellow ones)—notions like "we only register l33t with GitHub cred" and Ebay-esque star ratings not withstanding.