That is, I think Greg and Sam were likely fired because, in the board's view, they were already running OpenAI Global LLC more as if it were a for-profit subsidiary of Microsoft driven by Microsoft's commercial interest, than as the organization able to earn and return profit but focussed on the mission of the nonprofit it was publicly declared to be and that the board very much intended it to be. And, apparently, in Microsoft's view, they were very good at that, so putting them in a role overtly exactly like that is a no-brainer.
And while it usually takes a while to vet and hire someone for a position like that, it doesn't if you've been working for them closely in something that is functionally (from your perspective, if not on paper for the entity they nominally reported to) a near-identical role to the one you are hiring them for, and the only reason they are no longer in that role is because they were doing exactly what you want them to do for you.