4 days
The little advertisers aren’t the scary ones. It’s Meta, Alphabet and Amazon that are scary and absolutely do fingerprint in this way. That said, the scale of these systems really does roll right past the individual user, unless someone really cares about YOU, but unless you’re doing something wrong, they don’t really give a shit. CSAM, illicit substances, amd more could probably be pretty easily rooted out by these systems, but that wouldn’t make-line-go-up so it doesn’t happen.
Because money. It cost tax dollars to roll a truck to these sites every time a switch needs to be thrown. I heard that an air raid siren went off not too long ago because some kids figured out that they were controlled by DMTF tones on an unencrypted radio frequency.