It can’t be all bad, but it’s clearly not all good either.
It kind of makes sense that the people still there wouldn’t have bad stories to tell. What do you think is the worst part about working for Amazon?
Spending the money to recruit the employee, then pay them for a year or two, only to lose this talent is a great way to light cash on fire. That ain't cheap when your talking about hiring software developers!
It's relatively common that people don't make the cut during their probation period for example. Amazon (and other FAANGs) clearly isn't for everyone.
So I would question anyone that takes the easiest job they can find (their old job) after leaving Amazon in less that a year or two.