I had the same questions, and have learnt now that non profit governance is like this and that is why is a bad idea for something like OpenAI. In a for profit the shareholders can just replace the board.
>>crop_r+(OP)
Asking ChatGPT (until someone else answers) says that to remove a board member usually takes a super majority, which makes much more sense... but still seems to imply they need at least 4/6.