The Government also "tracks" large amounts of cash, which are about as anonymous, through audits - both random and based on red flags. Basically, they send round someone with the ability to lock you up if they can prove you've intentionally hidden assets from them, and they're very, very good at seeking out inconsistencies in your books.

Taxes existed before credit cards, you know.

Neither one is anonymous. In many ways they are less private than traditional currencies or assets.