In about 1985 I had an account at a British brokerage in Hong Kong closed since I had become a US person for tax purposes and the brokerage did not want to start filing paperwork with USG. The purpose of the IRS reporting, as I they understood it, was to create additional business cost to non-US banks and other financial service companies. If a bank had only one or two US clients it would still have to create processes to segregate all the client data of it's US and non US clients.