As someone else said you don't know that's wrong for what Amazon are optimising. If they find people [with your background profile] who buy shirts are susceptible to buying sweatpants, they might also find that if the seed you with "sweatpants" as an idea up front that the repeated presentation of sweatpants in "people who bought X also bought Y" sections is more effective.
That's the sort of thing I'd expect Amazon to be doing?
That's the sort of thing I'd expect Amazon to be doing?