Terrible targeting has a simple explanation.

Advertisers aren't incentivised to show you ads for what you actually want. They're incentivised to get money for showing you ads for what you plausibly might want, for the lowest cost possible.

And if you buy one thing and the algorithms go "finally! Some signal" you should be happy - it means you're hiding from them quite well.

Any "discovery" algorithm that shows you a wildly varying set of things is still mostly in explore mode. And if they're easy to tune out and swat away you can be grateful.