They’re probably using Amazon’s recommendation system which - at least in my experience - is pretty terrible with books. It might just be because I’m in the category of people who constantly get recommendations to buy things I’ve just bought and whatever puts me in that category stops them being able to make interesting recommendations, but it’s always pretty naff. I think the only good book recommendations I get from Amazon are authors I’ve specifically followed, or the monthly free early read choices which I don’t think are actually targeted at all