The CFO just preferred Windows, that's it, I'd bet money on it.
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?"
Excel has gone downhill massively.