It's good to point out this possibility, but outside of an institutional purchaser, people don't buy 2 mattresses with the purchases separated by a week.
Knowing that you bought a mattress is useful for the ML to find the mattress-purchase-likely cohort. Filtering those people out just saves the advertisers money. Hence the grift.
Knowing that you bought a mattress is useful for the ML to find the mattress-purchase-likely cohort. Filtering those people out just saves the advertisers money. Hence the grift.