When a company is privately held they need not file many reports that public companies must. Should they decide to go public they have to jump through lots of legal hoops before an IPO (Initial Public Offering) can be issued. They also would have to disclose many bits of information any company might not want to.
I know little to nothing about the stock market, however they were on the NYSE in the mid 1970's and I did consider buying a few shares of Colt Industries at the time just to have them. As I recall their stock was rather stagnant and I lost interest.