> it is almost always is something I don't want, already have, or just bought.

The explanation I have heard for the "just bought" scenario (I heard it on the internet, so grain of salt and so on) is that they're looking to catch people who purchased the item but have returned it, and are now in the market for a different version of the same item (e.g., you returned the chainsaw because it was too small, and now want a bigger one). Which makes sense, but whether there are enough people in that scenario to be worth the cost...