Bitcoin cannot be used as legal tender. Its price instability is risky, and its decentralization is difficult to control. Bitcoin will not be guaranteed by the government like fiat currency, it is insecure. Bitcoin users are a minority, and many people do not understand it but prefer to use national fiat currency.
price volatility makes bitcoin in some countries unsuitable for us to make as a legal currency, maybe that's the reason some countries refuse to accept bitcoin as a legal currency, and the government in my country never wants to accept bitcoin as a legal tender, because in my country there are still very many people who do not understand about bitcoin..