Given that he went radio silent since the voting out Altman fiasco exactly 6 months ago, it's clearly due to that.
One idea could be the product launch dev day, which is something that originally was a point of tension (overcommercialization vs research). Launching GPT-4o at a dev day basically asserts Sam is picking up no compromise on where they were 6mo ago. Good time to finally leave if protesting that is what he believes in.
Why not? We don’t know details that could involve financial agreements
cash out and live the good life? Start his own AI company or support company? Build the next better AI? The sky is the limit