Ask HN: Why signup rate is so low?

I'm getting 3k+ page views per month for http://railyo.com, a private job board for Ruby on Rails freelancers. The signup rate is extremely low (around ZERO) for client/company, (it is somewhat ok for freelancers) while most of the visitors come from Google Search.

What am I doing wrong ? Is it a bad idea ? Should I just focus on other projects ? Any suggestion ?