There’s no difference in regulations in or outside the city
> their institutions that isn’t there with some bank in a random backwater
It’s the exact same banks. Here’s a list for Jersey although the same is true for most Crown-controlled tax havens: https://en.m.wikipedia.org/wiki/List_of_banks_in_Jersey
I think the path dependency is what made the City of London the hub, and their trust system is how non citizens were able to access their financial system and those in their territories as well. I'm sure now there are ways to access services in these places directly now, but historically, the majority of the infrastructure dedicated to this stuff in these places was built out from England.