For one thing, mainstream bitcoin adoption of citizens can hurt the economy of a certain country. The fact that bitcoin is decentralized means that the government will not have any control whatsoever. Bitcoin technology allows the users to transact all across the globe and hold values with bitcoin without having to convert it to cash, this affects the demand for fiat currencies. It takes a lot of effort and time for a certain government to fully adopt bitcoin into their system. Needless to say, since bitcoin is very young and volatile, governments are still reluctant about promoting bitcoin to their citizens.