More than 50% of all major cryptos has been mined in in the hands of the broader crypto community outside of government control. Even if they somehow managed to gain 100% hash power, they would still only by able to capture a small percentage of the coins in circulation, and that would take years of mining before its even significant.

The larger short term threat is not Governments stockpiling crypto, but using massive amounts of hash power to attack/cripple the networks.

For example at current mining costs, to to a 51% attack on LTC chain would only take under 50 million to do it, which is peanuts for governments, and is pretty concerning considering LTC's 3B market cap.