Banks are still extremely oblivious to how powerful Bitcoin (and all other virtual currencies for that matter) is and how it will eventually start to prove their business model as obsolete.Banks fear bitcoin, because they see its potential. Many banks have looked into the blockchain technology and are trying to replicate it...purely because the technology is so powerful and out-does all banks by people preference by far. The only reason bitcoin has not taken over yet, is because of the peoples unawareness of it.
The reason why banking system in threatened by bitcoin because of the peer to peer transaction and decentralized system. The centralized system of banking system is the bread and butter of banking system in which they are the one who will market your money and asset and only part few percent will go back to the depositors they serve as a third party who will control your money.