One reason for FEINs on foreign bank accounts is because of FATCA, which is a bank regulation. Here is an IRS article with more information.
This IRS requirement (imposed on TurboTax), can also be explained another way:
Sometimes Foreign banks are present in the US. For example, In New York City, you can find many foreign banks such as the Bank of China, Sumitomo Mitsui Banking, Deutsche Bank, Bank Leumi, and MUFG Bank just to name a few. When these banks do business with other banks and Municipal / State or Federal governments, they would need to complete a form W-8ECI and use their FEIN. This is similar to a regular domestic business using a W-2 and EIN or an employee completing a W-4 and providing an SSN. Also they can't issue 1099 forms to US customers if they do not have an FEIN. According to your logic, though the foreign bank is standing on US soil, since they are foreign, they should not have an FEIN. However, there are treaties involved and complex tax issues that mandate that if services are provided in the US, then an FEIN is required.
This is just one example of why a foreign bank would require an FEIN. TurboTax is just complying with IRS tax laws.
@Anonymous
