Imagine if you were the CTO of a company, massively underestimated your AWS bill, and presented your board with something enormous. Maybe something like that happened?
Or, if I wanted to speculate to the extremely negative; what if the training and operating costs ballooned to such a degree, that the deal with Microsoft was an attempt to plug the cash hole without having to go to the board requesting an enormous loan? Because the fact that Copilot (edit: previously known as Bing Chat and Bing Image Creator) is free and ChatGPT (edit: and DALL-E 3) are not should be a red flag...
Microsoft is investing billions into OpenAI, and much of it is in the form of cloud services. I doubt there was a surprise bill for that sort of thing. But if there was, and Altman is the one who ordered it, I could see the board reacting in a similar way.