He basically broke the mission statement and wasn't forthright about it. OpenAI was founded as a counter to the giant Google. Instead Altman took the company towards max profits and signed away half the company to the dark side. Apparently the board had a problem with that, though one does have to scratch their head and wonder how the board didn't see this coming?
They did see it coming. If you look at the org-chart posted above, they have multiple layers of "control" over the profitable portion.
They just underestimated the power of money and the influence derived from it.