Once you deposit money in banks the money is not your anymore. You are giving the money to your bank with a promise they will give you back anytime you want. People are interested to use bitcoin to have a complete control over their money, without the limitations banks have
One of the strongest appeal Bitcoin has, is its ability to empower its holders to take charge over their finances and direct it wherever they deem fit. Last time the authority in Greece were able to stage a daylight robbery by helping itself to part of people's deposits in banks. You can't see such madness with Bitcoin.