The vast majority of the time it’s a big deal, which makes it newsworthy. As well, any well run company would announce at least a few quarters in advance that the CFO is leaving.
They don’t abruptly quit or get fired after 13 years without something brewing
Actually the vast majority of the time it's not at all a big deal. The average tenure of a CFO among the S&P 500 is 3.5 years. It's really not a big deal.
You must be new here. Many companies keep ex-C-levels nominally employed as 'consultants' so their stock can vest (which is typically the bulk of their compensation) and avoid any expensive/public lawsuits. It's paying them off to quietly go away without spending any cash.
This isn’t the own you think it is. C-level execs are often contractually obliged to serve out lengthy notice periods, a quarter and some change is nothing unusual.
They don’t abruptly quit or get fired after 13 years without something brewing