It does pose an extremely legitimate threat to their power, but there is nothing they can do about it. They can't stop it. They either embrace bitcoin or suffer economic collapse.

The only reason there are so many fist currencies is because no country wants to be using a currency that another is printing for free.

With bitcoin, that's not an issue and countries like El Salvador, Argentina would happily use it as the basis for a currency and thrive because of it. Over time, societies that use the best money win.