I'm also surprised that this is so hidden from everyone. Where are the engineers leaking secrets? Much of the online discourse is pure speculation based on what can be observed from the very end of the chain. (ie, what your computer is giving up) The speculation is not necessarily _incorrect_ but is too vague to be useful to anyone. Where does my data _actually_ go? Does anyone know? Can anyone describe the life of my data as it goes through the whole ecosystem? Does anyone know what mitigations are, and are not effective?
Because what's the headline you're going to get out of it?
If the headline is "Mark Zuckerberg is amassing your data and you know it's for evil", it's an easy sell. If it's "there's an ecosystem of little-known companies that sell transaction, location and lifestyle data to marketers, journalists, PIs, and police departments alike", it's not exactly the kind of a message that spurs people to action. And yeah, the newspaper that would be breaking the news is a customer too.
Despite being near universally hated externally, data brokering is a boring industry and is seen as very mundane and routine. They don't attract the type of engineers that have a strong moral stance and will go rogue and blow the whistle. They attract the middle age suburbanite just trying to get through the day and make a living.