I'm not sure if you're half joking, but banks authentify every single tenant in the transaction (from account owners, to institutions) in the most rigid way. Fraud usually happens at the edge (credit card), but everything "inside" the system is a legally registered entity.
It is completely integrated with the legal system.
They do solve the consensus problem but don't have the same constraints crypto does.
The consensus (of who owns what and how did that happen) is whatever the banking says it is at the moment.
This works because society places a lot of trust in the actors and the checks and regulations surrounding them (e.g. liability regimes) as well as the ways to rectify mistakes (through the legal system).
Crypto adds the additional requirement that every participant of the system (even end users) can independently come up with the same state without a single entity being the arbitrator of truth. The tradeoff is added technical complexity and inefficiency (storage and computation)
