AWS engineer here and I confirm everything you say, but this quote really struck home with me.
The thing I've noticed at Amazon is that not only are the pre-existing conditions awful, but nobody has any interest or willpower to fix it. Everyone will happily vent to you and tell you how awful things are, but any suggestions to fix it or make things more efficient (even if the fix is very simple and requires low effort) will be met with hostility. And I'm not just talking tech issues, but also process/workload issues.
I've worked across multiple teams and there is an "institutional ego" at Amazon where everyone, especially L7s+, think that Amazon is the best/smartest company in the world and have an attitude of "if Amazon, the best company ever, hasn't already figured out a way to solve this problem, then it must be an unsolvable problem and we won't even try". The thing is, a lot of these problems are in no way unique to Amazon and many other companies across the world have already found fantastic solutions to reduce things like on-call load. But adopting those solutions would require admitting that other companies were able to solve something that Amazon hasn't, which would hurt the ego.
This all applies to the very issue being talked about in the OP, too. Even managers will vent to you about how their team goes through 50% attrition every year, and how everyone is overloaded and finding new engineers is hard. They just accept 50% attrition as "something that just happens every year" as if having such a shitty team is normal, and there is no movement at all to fix it.