One of the issues with blockchain, at least from the POV of gov., is that a truly secure blockchain needs to be decentralized. A centralized blockchain is vulnerable to the same attacks as a centralized database.
And how do you (the government) secure your own permissioned blockchain without giving away the very power you're trying to maintain? I believe that the beauty of the technology is that it's most secure and viable when decentralized, thus rendering it useless for governments.
Ahh, I love it.