That's funny, because from the other things you said:

There is an intense pressure to force a certain amount of attrition each year.

As an SDM, I wanted to maintain the illusion of great Amazon culture for my team.

It sure looks like this wasn't the case of a "lazy manager" at all -- rather, that manager was doing exactly what they were told: to force attrition for attrition's sake, regardless of objective performance criteria. In fact, at Amazon that manager would only be seen as "lazy" for not meeting their attrition quota.