Amazon knows I just bought a fridge. How many fridges per month do they think I need? I keep receiving fridge ads and even on their own website, when logged in, they show me fridge offers.

Perhaps the intention is for the purchase to stay fresh in your mind so you're more likely to mention it to other people?

The ads drove you to post here and as a result, I'm reminded amazon is an option for white goods.

Taken to an entertaining extreme, one advertising approach would be to make ads as noticeably terrible as possible so people complain about them as much as possible.

It's almost as if, no matter what these advertising networks do, you can always reason in hindsight that it profited someone ...

It's almost as if, because it's rumoured to have powerful, dark & unknowable Machine Learning behind it, people assume it must be doing something reaaaaaally clever, and we're just not clever enough to realise what it's truly masterminding.

You're right in the specific case of Amazon and that product type: their advertising should definitely be more intelligent in that case.

more often than not, the merchant is the advertiser.