I mean, why would a bank care about phone numbers outside of the country it serves? Do you expect a US bank to recognize the number systems of every single one of the 195 countries out there when 99.9% of their customers live in one? Do you expect a French one? An Ethiopian one? It's not like they lose a whole lot of business if they don't support it; it's an edge case at best, especially when most people do get new phone numbers when they move.

And Google certainly knows you live in a new country, but you likely have to accept new Terms based on the country you move to, and there are more than likely fraud policies in place specifically to prevent people abusing a system like that to get lower pricing. The required step is there as policy, not a technical necessity.