Every major field that's taught in university has vastly more information than can be taught to students. The STEM fields are hardly unique that way.
What's odd is that the science and technology majors make an effort to push students as hard as possible, and the other majors choose not to. Look back on the standards at schools 100 years ago and you'll often see that the liberal arts curium seems way more difficult and thorough than it is today.
People underestimate how much is spent advertising to them. At one point the New York Times had an article on Facebook that noted you were only worth $5 a year to Facebook, when the NYTimes was getting $1000 annually per subscriber with their "declining" print business.
Would you pay $1000 annually for the New York Times? Probably not. Newspapers used to be very expensive and people rarely bought them. The model of putting ads in them caused a huge surge in sales. The ads were annoying as hell, they didn't cost you anything personally.
There are paid competitors to many Google products. People chose to use free versions with ads instead.
The behavior tracking services that I've seen also anonymize it . They generally require that you use some gibberish ID for the person, or do some sort of ID sync where you tell them what IDs you want to use for each person.
Where you often see a mapping to individual humans is with opt-in databases. Think of the act of signing up for an Amazon account, Safeway card or something similar. You've told them your name and where you live and they know exactly what you've purchased.