For example, a government announces that it will accept Bitcoin in that country, so I'm sure the development of Bitcoin in that country will be very fast!
What do you think, the Government or the community who play an important role in the development of Bitcoin?!
It's not that easy as you think just by merely announcing that your country will support cryptocurrencies is way different if the government has really done anything to do with it. We have seen it in the past, a government will announce big project or give promises only to find out that there are actually no real developments backing it up. For the "development" to take place the government needs to really show the support physically by action and not only words coming out from their mouth.
No government will actively support a decentralized cryptocurrency. It simply does not need it. Moreover, such a cryptocurrency is contrary to the functions of the government. It will allow the circulation of cryptocurrency under pressure from people, but it will not actively support it with various measures. On the contrary, over time, it will try to limit its circulation by introducing more and more new rules.