I've posted this many times, including http://news.ycombinator.com/item?id=3753915
They were required to make disclosures but no one forced them to go public. Plenty of companies have more than 500 shareholders yet still opt to remain private.
> Companies with more than $10 million in assets whose securities are held by more than 500 owners must file annual and other periodic reports. These reports are available to the public through the SEC's EDGAR database.