For what its worth, it seems like the board is claiming that Altman's constant wheeling and dealing of the technology, including giving Microsoft a minority stake in the LLC, rubbed them the wrong way, and they felt that his increasingly transparent desire for profits was antithetical to the original purpose of the OpenAI Non-Profit, which was to safeguard AGI, not to market and sell it.
Honestly, I felt that way too, so I'm on the boards side with this one. It felt pretty clear that Altman had tossed out the "beneficial for humanity" goal in favor of "beneficial to me and my wallet."