Bank examinations, like the recent "stress test," yield information of interest to the market. Releasing those results may increase transparency. For routine annual bank exams, however, doing so could impede a supervisor's ability to collect information.
Prescott, Edward S. "Should Bank Supervisors Disclose Information About Their Banks?" Federal Reserve Bank of Richmond Economic Quarterly 94, no. 1 (Winter 2008): 1-16.
Press release and related links on Board of Governors web site about the stress test results