What's going on here is that Amazon, Google, Facebook et al. know much more about us than we know or suspect at any point in time, because they're always advancing and all we can do is react and speculate when and if we notice something.

I suspect that, with the advertising/tracking and hardware/infrastructure ecosystems that they all are growing, they probably "know," or have at least recorded and have it available to analyze with each incremental capability advance, every audio, video and digital utterance and act we have ever committed since $DATE, and on into the future.

Who needs the NSA when you have the FAANG?

(Exactly how they do it, which was your question, I don't know.)