Because it doesn’t work with business accounts. Or joint accounts. It’s basically unsupported at this point. This quote from this thread basically sums it up.
Of the two original authors @simon has now left Monzo, leaving just @kieranmch. As far as I can tell there’s no team dedicated to it, nor anyone really responsible for it. This is a crying shame because Monzo should really, imho, make this integration rich and full. A wonderful project that sadly doesn’t seem to have gotten the buy-in from whoever has the power to allocate sufficient resources to it within Monzo.