I suspect that's because those are the only things that are easy to model. People buy them: a) based on personal taste b) in volume I just bought a ladder on a

I suspect that's because those are the only things that are easy to model. People buy them: a) based on personal taste b) in volume I just bought a ladder on amazon, what information does that tell them? Since it's the only tool I've bought from them it doesn't tell them much. They now know that I might be willing to buy more tools from them in the future but doesn't help in targeting which kind or how often. Me being a ladder buyer is a very weak signal that I will buy any particular item from them. If on the other hand, I've bought 15 Aubrey Maturin books from them over the last few months, it doesn't take the most sophisticated model to determine that I probably want to buy number 16 next. Or that I might like to read the Horatio Hornblower books.