My standard response to this: Prior purchases do have predictive power. They can very well be positively correlated to further purchases.
I've often bought stuff that didn't work for some reason. It was broken, or it had something that was bothering me. Maybe the power adapter was annoyingly loud (looking at you, Kyocera).
So I sent it back. But before I managed to go to the postal office a few days later I was already searching for a replacement online.
If I buy a TV set, I have indicated that I need/want a TV set. The rate of returns is broadly known (and maybe even specifically for me the return rate is known).
So Amazon et. al. do well to recommend similar stuff or things from the exact same product category to me.
Even right after I have bought a graphics tablet I'm infinitely more likely to buy a graphics tablet tomorrow, compared to my parents who have never bought one in their lives, and never will.
Or maybe the new TV turns out to be great, and I realize it would be nice to have a second one in my sleeping room, and why not buy a third one for the bathroom? ;-)