Why do Banks vigorously oppose the use of digital currency?

A digital currency is any type of payment which is in electronic form and is accounted for and transferred using computers. Examples of digital currencies are cryptocurrency, virtual currency, and central bank digital currency. Well known cyptocurrencies are Bitcoin (BTC), Ethereum (ETH), Litecoin (LTC), Dogecoin (DOGE), Polkadot (DOT), Stellar (XLM), Carnado (ADA), and Bitcoin Cash (BCH). I am researching cryptocurrencies and would like to know why Banks forcefully oppose the use of digital currencies. Any sugestions would be very much appreciated.