This is all just business, right? If you're holding the nut flush and you think the board's got rags, you play it out. Whatever reasons the board had to be done with Altman, they did not have the cards, and he did: the team, as I understand it, believed itself to be dependent on Altman (or at least, on not-the-board) for their stakes to be worth anything.
I see how it'd be really dicey for a CEO to pitch a fit on the way out under ordinary circumstances. But also, if you fire your CEO, he may very well go stand up a terrifying competitor, which is basically what happened here, right?