I can't really speak to amazon retail, but in my 7 odd years in aws I found most people left because
* working in infrastructure means doing a lot not quite so exciting things. most people aren't actually excited by ops, and a lot of your dev work will be on ops. its also the case that ops was historically not as well rewarded, though thats been fixed
* every service needs to be held to the highest tier of operational excellence, and so you can't just chabuduo when things aren't working as well as they should. in the worst case, this means throwing bodies to the ops meatgrinder.
* delivery speed is slowwwww. some of this in endemic to the space, but aws at the end of 2021 (when i left :) ) was a lot slower than than when i joined due to so much risk aversion and bureaucracy
* comp wasn't as good compared many tech peers, and comp could very easily not keep pace if you weren't tippy top every year. this is imo the most self-defeating part of amazon culture as a whole because it incentivizes people rated between ~p10-p20 and p50 to leave.