Its not just the USA, Hitwise claim they have data from 8 million UK subscribers if I recall correctly.
If you have an online presence, a web site, an ecommerce business... UK ISPs consider they have the right to scam your copyright content ,and sell marketing intelligence about your visitors and customers to third parties... so that your competitors can benefit from your efforts.
Its automated mass industrial espionage.
If it were happening to telephone comms, you would expect people would be jailed.
Its no different for web traffic. Web comms are private point to point connections between web sites/online businesses and their visitors and customers. Not some kind of broadcast.
A communication company stealing that data and flogging it without the consent of either party is simply utterly illegal.