Says who? According to the torproject.org homepage, the purpose is:
> [to help] you defend against traffic analysis, a form of network surveillance that threatens personal freedom and privacy, confidential business activities and relationships, and state security.
That includes stuff like preventing your ISP from knowing private personal details like how one was fired, or is secretly gay, or likes to write or draw porn, etc.
Also, if you own a big business and you just bought a supplier to eliminate the costs of a middle-man, you might also want to keep that confidential from your competitors for whatever business strategy you have.
The US Naval Research Lab that developed onion routing, patented it, implemented it in the form of Tor, and released it under a free license, which is how the outside-of-government (though founded by some of the same people who had developed the tech and implementation at the USNRL) Tor project was able to build on it.
Edit: On further reading the distinction is the TECH behind tor was created for that purpose, TOR itself was created for what it says on the tin.