Per the article, in exchange for that goodwill they get a billion dollars per week. Do we need more explanation?

To be clear, it's gross, but they are doing it just enough that their convenience and average sufficient product quality keeps me using them. I'd guess they do a lot of research to keep that balance where it is.

I don't expect to get any sort of explanation from Amazon of course. I do think they are probably doing something that is hurting them financially. Acquired goodwill is extremely hard to measure and shows up in things like long-term customer retention and engagement, so you're not going to see it on an A/B test -- on a A/B test users come in with the same level of goodwill on both sides of the fork and thus their immediate behavior is not going to be dictated by this.

In many ways this is symptomatic of larger trends in society and managerial culture of looking for ways to measure things rather than confronting the messy subjective non-measurable reality.

The only time we'll get a true counterfactual is when a competitor arises who can meet Amazon's very high bar for logistic excellence but can offer a more appealing interaction, and then Amazon retail will die off without anyone understanding how or why it happened.