So, to be clear, you can’t actually liquidate your account.

No, it’s that it is incredibly rare for someone to actually want to liquidate their account because the reason people do is usually to move banks and that use-case is better served with a cashier’s check. It’s not at all surprising that random branches don’t keep that much cash.

You can always liquidate your account. What you can't do is make it some random branch's problem in a spur-of-the-moment decision; you have to plan it with them.

No, that doesn't follow. You can definitely remove large amounts of cash, you just have to think ahead a little. Also, you have overlooked the fact that for many people a cashier's check is more convenient than a large wad of cash, especially if their sole object is to deposit it at a competing institution.