For many users who love security, the shutdown of Truecrypt was a big surprise. One of the major reasons that users of Truecrypt were so surprised was because the developers left the users in the dark. No one knew what happened, why they shutdown, all we were told was that it is no longer recommended to use Truecrypt by the developers. The shutdown of Truecrypt occurred during a crowdfunded audit to make sure it is safe to use. The audit did not find anything, but in more recent times a security issue has been discovered. The issue that the audit missed was that anyone with a user account could get access to higher level privileges in the system. This issue has been fixed in the forks of Truecrypt such as Veracrypt, so you are safe to all current knowledge if you use Veracrypt.
Could this be the reason that the Truecrypt developers decided to shut down the project? There are countless rumors and ideas that are floating around the web, each one getting us no where. But this recent discovery is another clue in why they shutdown.