“there was nothing in the community that was interesting to me”
This why most people don't participate.
So what’s interesting to me? There seem to be three universal discussions.
1) Discussions about me. Discussions about ourselves, our company, our jobs, the work we're doing, the things we do, or the things we want to be/have done.
2) Discussions about what I know. Discussions about topics I feel I'm an expert on and topics I feel passionately about. These are the discussions I can contribute to. The greater the level of our expertise in a topic, the more we're likely to participate.
3) Discussions about who I know. Discussions about those we consider our peers. Discussions about our peers, their work, and their successes/failures are likely to be very interesting to ourselves.
If members aren't interested in your existing discussions, make the discussions about them, what they know, or who they know.
Ask them who they are, what they know, and who they know.