Bitcoin is not a regular currency because it is limited in supply, the government does not want to have this kind of system in place as for sure there will be a problem of shortage, when there is a shortage they can easily print money while it's not possible in bitcoin as it is design to have a fixed supply.
Bitcoin is not just a currency because of it's limited supply, it is also an investment so it could be an asset or currency depending on how you define it.
Yes, this is also a problem for governments and its central banks that if they need more bitcoin, it is not in their reach that they arrange the supply. Because it is not paper currency and they do not print it. So, I feel that any central bank of any country would not be able to fulfill the demand of the people for bitcoin. Thats why they do not take any part in bitcoin mining and anything else related to bitcoin.