They prefer the U.S. Treasury hold the lien

“A home mortgage is the most common example of secured debt in our society, but practically any valuable possession can secure a loan. We really do mean anything, tangible or intangible—a car, a collection of tattered law books, a debt that a third party owes to the borrower, the borrower’s rights under an esoteric contract (such as a musician’s right to receive royalties from a song each time it gets downloaded to an iPod), or a plaintiff’s rights to collect money from a lawsuit. Even a tenant’s interest in a lease or a farmer’s grazing rights on land can be pledged as collateral for a loan. Once you learn the legal power that a lender gets from having collateral, you’ll wonder why lenders ever loan money without taking a security interest.” – Nathalie Martin and Ocean Tama, Inside Bankruptcy Law (emphasis in original)