[ghaff]

It seems to be a general problem with recommendation engines.

I assume that manually tagging certain types of items with a flag that means "The buyer is unlikely to buy another item in this category within a meaningful timeframe no matter how often we recommend it" is more effort than the recommendation slot is worth. There are probably a number of flags one could imagine setting but it's likely very hard to automate because it requires understanding how people use/consume/upgrade/etc. a given item.