Because they are afraid to take risks, they think that the bubble can burst at any moment. And the state wants to control all financial operations.
They are not afraid to take risks, bitcoin helps a country economy, and I don't think it's price matter at all. Bitcoin is a decentralized digital currency so they can't control the bitcoin transactions. There are many reasons that the government are not accepting bitcoin, but I know time will come and they will be changing their minds when they see how bitcoin helped other country.