IMO this is increasingly the most likely answer, which would readily comport with "lack of candor" as well as the (allegedly) provided 2 explanations being so weak [1]: you certainly wouldn't want to come out and say that you fired the CEO because you think you might have (apparently) dangerous AI/AGI/ASI and your CEO was reckless with it. Neither of the two explanations seem even to be within the realm of a fireable offense.

It would also comport with Ilya's regret about the situation: perhaps he wanted to slow things down, board members convinced him Sam's ouster was the way to do it, but then it has actually unfolded such that development of dangerous AI/AGI/ASI might accelerate at Microsoft while weakening OpenAI's own ability to modulate the pace of development.

[1]: Given all the very public media brinkmanship, I'm not so quick to assume reports like these two explanations are true. E.g. the "Sama is returning with demands!" stories were obviously "planted" by people who were trying to exert pressure on the negotiations; would be interested to have more evidence that Ilya's explanations were actually this sloppy.