> When you "transfer money" from your bank account to another, your bank has to physically move the associated cash from it's vault to the other banks vault, by hiring secure trucks, people, and so on

That's several centuries out of date, I'm afraid. Even before computers banks didn't actually do that, but now they certainly never do that. They just change records in their books - it has been paper books once, now it's just database files. I mean, banks do move cash (still do) but not when you transfer money from account to account, it has nothing to do with that, unless when you're running a massive cash-based business (which most banks hate btw, for many reasons).