Now, the question: why it takes THAT long the smaller banks to go the same way and start using the blockchain?
For any company or banks to implement a new technology you need to have a thorough understanding of the system and you cannot implement all the all of a sudden and majority of the technology companies are learning about the opportunities of blockchain for a long time and if the banking sector find it useful for their business then they will implement it.
Of course blockchain will be helpful to banks even growing banks that are not established already. It will help them to secure data and security information that are already stored in their system. Blockchain technology is already being used in certain places and banks shouldn't be an exception.