Either he really was the wrong person to lead openai, or the exact right person but the board couldn’t go along with his view for ethical or financial reasons.
My guess is he's the right person to run closedai, but not openai. Board has no financial interest in the company, and wanted to stay true to its initial goal.
If this was true then it could have been done as an agreement that Altamn would exit over a number of months or so. No need for it to be immediate.