It's not that baffling; Microsoft is selling Office 365 for Business for corporate accounts, and Office 365 Home for personal use, and expects users who have access to the former for corporate use to also have the latter for home use. Indeed, their Home Use Program which used to let corporate users let their employees purchase similar-level standalone products at a sharp discount to use on personal computers now has the primary option being a discount on Office 365 Home.

So, that it makes perfect sense that the personal finance solution that they intend to be a motivation to buy Office 365 Home isn't available on the Office 365 for Business accounts many of the people they want to sell Home to also already have access to.

Exactly - this is a silly choice. Making it inaccessible to users of Office 365 for business is a terrible default choice.

That does seem silly on principle, but I doubt many Office 365 for Business users actually need such a thing anyway. Maybe it's some kind of bug or oversight?