According to someone from NETCOM, it's because the leaks are still classified. Therefore, unclassified networks within the army must block the leaks in order to maintain their operational goals of no classified information on those wires. They have separate classified networks, which surely allow it.

There's an old saying... There's the right way to do something, and then there's the Army way.

    The Department of Defense routinely takes preventative “network hygiene” measures to mitigate unauthorized disclosures of classified information onto DoD unclassified networks.

    We make every effort to balance the need to preserve information access with operational security, however there are strict policies and directives in place regarding protecting and handling classified information. Until declassified by appropriate officials, classified information—including information released through an unauthorized disclosure—must be treated accordingly by DoD personnel.