The reason why banks exist is because they can do credit creation by issuing loans. This enables a bank to lend out more “money” than reserves at the central bank and other assets. Crypto is like “gold” and if it becomes more common in everyday transactions it would mean that banks would have to build up crypto reserves, in case they start having accounts denominated in bitcoin. This in turn enforces central banks to hold crypto in case banks have to be bailed out if crypto becomes very common.