There are a lot of different kinds of financial institutions with a lot of different kinds of needs. In general, however, functional languages are a good fit for highly regulated domains, because they encourage splitting the (stateless) business legal rules for the domain from the stateful data management.

Complecting the two into, e.g. an Account object that has both metadata related to an account and e.g. rules related to transactions that can be part of an account quickly turns into an expensive maintenance nightmare.