If it's traceable, how is it anonymous? I.e., you could have a wallet full of BTC that no one knows is yours, but the moment you buy anything with it that's linkable to you then all of your BTC becomes non-anonymous.

If you put every incoming transaction into a separate wallet, and create a new intermediary wallet for every outgoing transaction, then only a minimal amount of Ⓑ becomes non-anonymous with each outgoing transaction. But statistical methods can still probably bear fruit.