Well, because the government has a contract with the PFI people, but obviously doesn't have contracts with its own employees. Oh, no, wait.

Maybe it's because cancelling PFI deals would result in corrupt rich people who don't pay tax not getting as much money? After all, we're regularly told that it's necessary to give those people as much money as possible, preferably at the expense of much poorer people. Otherwise, they'll leave the country and not pay any tax. Um, or something.