There is essentially no point to using a blockchain if the only thing you're putting on it is an accounting system you have absolute control over anyway.

I think tech people vulnerable to buzzwordism have an instinctive response to respond to any mention of money with "blockchain!", even though it's really only useful in this context for decentralized payment systems (i.e. not for banks). The only place banks might want to use blockchains is for low-trust inter-bank settlement.