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 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.
There are many big companies or brands that understand crypto currencies of blockchain technology in detail and even are investing into digital money. As far as banks are concerned, I am pretty sure all banks are aware of blockchain technology because they are already dealing in stuff that is related to economy or in short money. I am sure there will be banks in future offering their services to crypto users.