From Amazon's perspective, it doesn't have to work for you; it has to work on average.

In that case, it may be better to just put the hot new item in a category they know you purchase in. For instance, if I have a subscription to paper towels, maybe they should send me a subscription recommendation for toilet paper.

I'm sure someone thought to A/B test the recommendation engine against the whatever-happens-to-be-selling-right-now engine and the recommendation engine won.

An AUC of .5 isn't considered good in ML

That very much depends on the domain. In this case, I suspect it would be considered phenomenally good since a human would achieve a much lower number. Conversion rates for web ads created by humans are typically not more than a few percent.

Amazon also doesn't know if this is a single use or consumable item. Some things have significant marginal utility beyond 1, and others can be consumed and need to be reordered. (Charging cables, Amazon echo for multiple rooms, paper goods, etc.)

How often do I buy a HP Color LaserJet printer, versus toner cartridges for it? Or ink for another printer of which it has no evidence that I own)?

Yet I bought a color laser printer and my first two pages of recommendations are for other variations on the same ("Hey, you bought the wired MFP! Perhaps you want the wireless too! And I know it's a HP printer, but maybe I can suggest some Brother toner for you!").

You're correct that Amazon should be smarter about some recommendations. I'd say give them the benefit of the doubt in that they may have found an algorithm that works most of the time (or at least when it comes to their bottom line), but edge-cases stand out to us.

Still though, there could be a method to the madness. You bought a printer - are you setting up a home office? Perhaps you want a second printer for upstairs?

Also, you just bought an HP brand printer. Were you replacing a printer that just ran out of ink? Maybe THAT printer was a Brother printer. Perhaps this Brother ink cartridge can extend the life of the hypothetical printer you may be replacing...

My point is that I can contrive cases where the recommendations might make sense - not to you, specifically, but to a large enough cross-section of consumers.

I don’t doubt there are entire divisions in Amazon that draw statistical correlations and do A/B testing to figure out what annoying emails work. Just like any other marketing agency. So you can be sure that any annoying email you get is the probably the result of years of metrics.

Bad example, because printers often are consumables. ;)

If you buy the printer that is "consumable" more than once, you deserve it :)

You made my day :)

Agreed.

They should have a pretty good idea which items get reordered a lot and which don't. They've got plenty of data.

Amazon should know - can't it munge peoples shopping records to spot patterns.

Like mentioned in a sibling comment, I bet Amazon could very easily deduce that toner is sold a lot more often than actual printers.

Yes, they do. Customer patterns on that product

They could use some of this vaunted machine learning to figure it out.

That’s assuming those are the alternatives. If the alternative is instead to show you something you’ve already ordered or nothing, the odds of you ordering again if you see the thing you’ve ordered already are small, but nonzero.

That's a false dichotomy. There's a number of things they can show you, not just reorder or nothing.

In a perfect world for targeting sales, they will predict and show you exactly what it is you want to buy next. Repurchasing is just a very lazy way of predicting what you'll buy next.

I'm not afthonos, but I think his/her point is that they may not be able to predict exactly what it is you want to buy.

(I find it super annoying, too; but that doesn't mean folks have figured out purchase reco's at scale)

If the chance I'm going to buy something that I've already bought again is close to 0, and it's not smart enough to find anything else for me that it thinks I should buy, then logically it should show me random things. That way I'm training the algorithm for them and maybe I'll find something I want.

Logically, they will show you whatever is most likely to generate revenue (possibly amortized over time). As long as the probability of you reordering is higher than that if you buying a random item out of millions (and those odds are tiny to begin with), the logical thing to do is to show you the item you already ordered.

People buy a lot of consumable products on Amazon. People buy a lot of things and realize how much they like and would like another for another room in the house or something. You aren't thinking broadly enough here.