Frankly, because it’s not as much of a threat as the popular narrative suggests. They may actually benefit from being able to use cryptocurrency for their own ends, either by using it directly or using the public ledger nature combined with their surveillance powers to get insight into transactions.

Regardless, the attacks described here require large concentrations of mining power. In theory, the best way to attack it would be to wait for (or even encourage/subsidize) your country to become the geographical leader in mining operations.

Or even better: Wait for companies in competing countries to start holding BTC on their balance sheets and consumers to put their investments in BTC. Now you have a kill switch for part of the balance sheets of competing countries.

I personally doubt this is happening, but I’m sure it’s being considered as an attack scenario.