Statistically this works out pretty well.

If you spent real money on something, you're far more likely to buy it again or buy it for someone or send that link to someone than a completely new product.

Do you really need an ad to get you to do that?

The question is, rather, does an ad increase your chances of doing that by 0.1%?

If yes, it suddenly makes sense to show the ad to the ~1000 people in your target group.

Even worse. It doesn’t work. Yet, it either way requires large scale harvesting of everyone’s personal information.

If it wasn’t allowed, the value of all this personal information wouldn’t be as high.

I thought it’s idiotic until the first time I sent something back for a refund.

And how many times did you do that :))

The great thing about them selling you something made to be as crappy as you will stand, is that then you'll then have to refund it all the time, making their re-targeting ads even more "effective" :)) What a virtuous cycle!