Consider that is mostly public headway. Behind the scenes the handover, mentorship, alignment I am sure was already happening for a while. E.g. you probably don't want the incoming CEO to have to immediately clean house or people might end up doubting their decisions, getting anxious or similar. The previous CEO can start retiring, moving people around to clear out possibly problematic leaders, break up internal "gangs" and ways of work - people will be more willing to accept their decision as they've been at the head for a while and have the trust. The new CEO comes in, group dynamics and rules are still fresh and building up between everyone, they don't have a black mark for firing anyone - to me it just feels like it would be a healthier and more mature transition.
To support this I was thinking about (and obviously Googling these names because I definitely don't know them by heart, only that they recently left) the change of CFO Luca Maestri to Kevan Parekh, John Giannandrea being removed, Alan Dye leaving and being replaced with Steve Lemay.
So I take those 4 months more as like an FYI to the public than anything else. Though I am definitely not someone that knows corporate politics all that well (or at all), just mostly thinking out loud in response to your comment.