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...
and
"no longer has confidence"
points to something more serious than underestimating costs.
Maybe Sam had been trying to broker a sale of the company without consulting the board first? All speculation until more details are revealed but he must've done something of similar magnitude.