[Closed] Website's recommendations algorithms - has anyone managed to make them work?

Why do all these website immediately recommend the exact same product, or service, or location of the thing that you've just bought from them? Just been to Namur for the CX - am now getting emails telling me that it'd be cheaper to go next weekend.... But I'm unlikely to go back again, unless we feel like going back to the CX again. Same as a Christmas present that I've bought for a relative - now getting emails from that webshop telling me all about how much cheaper/ better/ blue-er some other identi-product is.
Why is this?