It's pretty crazy that our legislators and courts haven't addressed this loophole that allows law enforcement agencies to buy data that they can't legally collect. This essentially nullifies the fourth amendment.
That said, it’s not a loophole. State and federal laws make certain data public or quasi-public for limited purposes, and I can’t think of any reason the government should be prohibited from buying it for one of those purposes. The fourth amendment is designed to prevent the government from collecting information that is distinguished as categorically private by definition.