where exactly are the ridiculous amounts of money being spent? a bank can implement their own blockchain by deploying a server in each region. they can mine with the server CPU because it is not an arms race to get more hashing power. with this small Blockchain network they can store all customers transactions in a decentralized and secure fashion. Remember the 51% attack is based on a percent of hashing power, all bank nodes can mine on CPUs to secure the network like we once did.
I think too many people are fixated on the Bitcoin Blockchain as the solution for everything. For internal applications where there is no hashing power arms race, creating a new network is a perfectly good application of the technology.
The point of hashing and the blockchain is attaining distributed consensus in spite of being open to the whole world. If it's for "internal applications", there's no need for a blockchain. An ordinary database will do and, as a bonus, won't be open to transaction analysis and network attacks like Bitcoin is.