Banks can use blockchain technology but it is never going to be in decentralized manner so it cannot be compared with the crypto adoption if banks starts doing transactions with blockchain.Either bank employees may not let it happen sice if the blockchain was introduced then most of the employment in banks will get vanished.
banks are government tools in the economy, especially those related to the use of fiat currencies and all systems are regulated as well as possible but as the times change and technology of course banks will also use a developing system as well and crypto currencies with blockchain systems that use advances in technology can will also be adopted by the government for the bank system