It's been a slow burn of this for years, but the Covid fiasco has given a lot of near-retirees reason to call it good and move on all at once. Not to mention that the capitalist economic system specifically disincentivizes workers from staying and building experience at a job in its current form, so you have people (professionals, but others too) constantly bouncing around all over the place cause it's the only way to get a substantial raise, which is obviously very efficient at scale.