I can think of plenty of companies that do plenty of things wrong, or at least seem to be wrong. I can't think of many things virtually all of them do wrong, especially ones that are so well publicized and are at the organizational level rather than the individual team level.
I can see equity being a reason for Amazon, but it is hardly just equity granting companies that are this way.
You call it out yourself; it may not even be "the company" is seeing much change in retention, but different parts of the org are. Others have solid retention.
But retention also isn't an easy metric to solve for. It's not "just do X and watch that number improve". The closest thing companies do is throw money at people, but that only works if you're so far higher than the rest of the market that people are looking at a massive paycut if they go somewhere else, and that still is only one data point affecting those averages. Certainly, no company that I left could have kept me by throwing $9k more at me; I made more than that with every company change I made, let alone what actually caused me to start looking in the first place.
I can see equity being a reason for Amazon, but it is hardly just equity granting companies that are this way.