Why, you might ask yourself, does the U.S. government purchase information from private companies in the first place?
There are several reasons.
First, The Privacy Act of 1974 places restrictions on the collection, use and dissemination of personal information by the government, but does not place limitations on the private sector. Therefore, in order to retrieve desirable information, government agencies turn to private companies that can freely maintain huge databases. By relying on the self-regulated business sector, the government can carry out privacy-invading practices at a comfortable distance.
Businesses also have greater contact with the public on a daily basis, allowing for more opportunities to collect more data. The government can bring together information from various commercial sources to produce a detailed dossier that it could never produce alone, making nearly every social interaction a ripe potential for data surveillance.
In 2001, with the passing of The USA Patriot Act, many legal restrictions placed on the government regarding data collection and use were relaxed, allowing agencies to simply demand commercial data free of charge. These requests can happen without judicial review and sometimes with a "gag order" on the targeted business--so you and I will never even know about it.