You'd be surprised how often that is not true for secondary and support services. In Canada we have many service providers (Interac and Symcor being two big ex

You'd be surprised how often that is not true for secondary and support services. In Canada we have many service providers (Interac and Symcor being two big examples)that are joint ventures between all the banks they service. So things like (historically) bill printing and mailing and more currently fraud detection and various digital transformation initiatives are being done by these service providers, so that the banks don't all have to spend money on the same stuff separately (and can interoperate more easily). As a bonus, they can also offer those services to other parties and increase profit for the bank owners.