The most popular misconception people have about creating a private online community is the work and upkeep behind it. You simply can’t dump content and run. Implementing a private online community with a robust feature set doesn’t mean your entire member base will flock to it immediately. (Even though it was free and there was no commitment involved, I turned down three Facebook requests to join when it first came out because I didn’t understand the value, at the time, in that sort of connecting.) It takes content, fun features and care/maintenance of someone in a community manager role.
Even the most well-constructed car’s color will fade, exterior will rust and its mechanics will cease to work when left unattended for years. Care and maintenance is required. You have to drive it (or at least start it) on occasion.
Content is important to your community but so are connections. Give your members a place to connect and something to do there. Something they want to do, not something you think they should be doing. If you are not thinking about what your members want and how they want it, your community will fail.