It's not but its a lot easier and safer to hold digital currency than wads of cash in your floorboards. Easier to acquire, receive from abroad and verify as well. It allows for a form of civil disobedience against unjust laws
All it takes is to turn one participant, and the threads can be followed to trace the money.
If I hold something in a digital wallet, I can never be sure I've eliminated all the ways to take it remotely and anonymously.