If you move money from one pocket to another, or one savings account to another (that you own), that's not taxable. Very many transfers between bitcoin addresses is just like that: the 'change' from a transfer goes to a new address owned by the same person.
Even when the addresses are owned by two different people, the transfer often isn't taxable. You don't pay a tax when you pay a bill, but that's a currency transfer between two parties. Even when you buy something it isn't necessarily taxable; in many jurisdictions many products are sold tax-free based on either the type of product or where the buyer and/or seller are based.
I don't think there's a way to enforce taxation on bitcoin that's not already being used to enforce cash sales taxes and cash income, despite the tracability of the coins, because the address owners may not be identifiable, and the nature of the transfer is definitely not identifiable from the blockchain.