Read a good a article about the history of the OpenAI board that argued this all went down due to the recent loss of 3 board members, bringing total board membership from 9 to 6 (including losses like Reid Hoffman, who never would have voted for something like this), and Altman wanted to increase board membership again. Likely the "Gang of Four" here saw this as their slim window to change the direction of OpenAI.
What I'm fairly sure of though is that if the board had been stocked with heavyweights rather than lightweights that this would have been handled in a procedural correct way with a lot more chance that it would stick.