My guess would be that, those people who were no longer growing at Apple, after six consecutive weeks off, filling their mind with things other than working at Apple, realized they had stagnated and figured out something else to do. It's much easier to have perspective on a situation after spending a significant period of time away from it.
HR people note that people often don't come back from them. I think that is in part because you do get to refresh a bit and think about things and ask really deep questions like "what do I really want to be doing with my time?" A lot of things change in 5 years.
However, the idea of letting people take an extended break to recharge is a good one, if someone comes up with a good way to do that without losing employees it would be well received.
Well, it's not 50K, on the other hand it was surprising how many people hung on until five years, took their six weeks off (often including vacation), then quit.
It seemed to get rid of dead wood. I'm still not sure why.