The requirement came from the investment house - they wanted data in the format they were accustomed to.

What was driving that requirement at the investment house doesn't matter, when the company that owns over 50% of your company wants something, you don't say "Hey, we don't want to buy a Windows license with your money, how about I send it to you in this similar, but different format and then you guys can figure out how to make it match what you're looking for?"

IME what it means is that they have a bunch of processes built that specifically depend on it. It doesn't make it impossible to switch but depending on the scope could be financially or practically prohibitive to migrate. Maybe someone has 10 years of custom excel macros put together that are run every quarter, that would need to be migrated. To migrate you might not have the internal capacity and might need to hire external help to do it.