If Google doesn't know what ad to show me, why not show no ad, instead of a scam?

Does trillion-dollar Google desperately need the 3½¢ of revenue the scam ad generates?

It's not that Google doesn't know what to show you, it's that no advertiser outbids the scam ad for your 30 seconds of attention.

To put it another way, you have next to no value, and it's only by the goodwill of Google that they even let you on the platform.

Goodwill doesn't explain why Google Ads will show scam ads on other people's web sites.

Yeah, it's wild how poorly the hackernewses understand this. If the ad platform has few signals for targeting, but it does have the available signals of you're using a weird VPN or tor, and a weird user agent on an uncommon platform, then it's just going to assume you're a crypto loser like the other people sharing those traits.

… I'll bite, then. I not only accept cookies in this case, I'm logged in. I get these same cryptocurrency scam ads.

The metadata for ads comes from external sources, such as Google AdWords embedded in millions of websites.