This is an interesting thread... We built several sites in a closely related niche market last year and some of them are wild-crazy busy as planned. Others, built with a very similar set of criteria, are ghost towns, similar to what you're seeing.
What platform is your site built on? Is it plain html, or are you using a CMS like WordPress or something else?
How is your internal link structure? Are most pages within 1-2 clicks of the homepage?
How is your external link profile? Do you link out liberally and often to other authority sites within the topic?