Their recommendations feel to me like the recommendation engine is still more or less the one they had when they were mainly an online bookstore. So they assume you want things similar to the item you bought: other novels in the same genre, nonfiction books on similar subjects etc. Works fine for books, less well for coffee tables.
Every year around burning man time it "notices" that I'm buying supplies for burning man, and starts recommending me things like baby wipes, which are completely unrelated (naively) to things like lag screws, rebar pullers, etc.
I suspect that's the impact of other burners also shopping, generating a good list of "people who bought A and B also bought C, D, E...". As soon as you hit A & B, you trigger the rest, while the average person doesn't.
