I'm not disputing a data broker sells data; I'm claiming that ad-platforms don't.
In general, those companies aren't interested in bundling up data on users and selling it to third parties because the data itself is the nest egg. They go out of their way to, if anything, provide services for anonymous matching of interested parties to users they've collected data on, but not in a way that lets those parties pull the data back out.
I agree - faang/etc do not need to sell the data outside their walled garden but there are tons of vendors with sdks in millions of apps and pixels on millions of websites that have considerable location/user data. It’s easy to find how to buy + activate that data which is the point I wanted to make.
It sounds like you just aren't aware of how deep a rabbit-hole the ad-tech space is. Google gets to be the relatively-clean "platform" at the top, but they don't exist independently of the rest of the industry.