There have been lots of other currencies privately traded previously, but since the state has the guns the state can outlaw it. If it truly started competing with major currencies you would see it outlawed. It also is not secure as China is controlling a majority of the mining now and the majority can control the currency. Further, Google has a computer that can hack the encryption and you will see a lot more organiz…
The state has the guns to outlaw a lot things. Yet many of those products, I can still purchase on the local street corner. Simply having a monopoly on force isn't enough to totally stop trade in some good. Especially when that good is easy to hide, and easy to move. Crypto is pretty much the easiest good to hide and move in the history of mankind.