The question isn’t “do they do it on a regular basis” it’s “do people do it often enough that the expected value of showing that product is higher than something else.”

> The only logical conclusion is that it's cheaper for them (in the short term, at least) not to update their ad/recommendation algorithm to take into account the nature of large one-time purchases.

Is that really the only logical conclusion? I’d think that “I don’t know people’s buying behavior on Amazon well enough to understand why this happens” should at least be a possible explanation.