I don't even understand the need for this discussion.

Even with old-style flat currency banks,
you can have one million $ stored in your accunt
but your credit card will still have daily/monthly spending limits.
And limits in the amount that can be withdraws from a ATM. Etc.
You can't withdraw one million in a single operation from a ATM.

That's for your safety so in case one steals your card and password,
they can't empty your account very quickly.
Which leaves you a chance to lock your acount and limit the damage.