It blows my mind how much of the internet economy is built on sucking up user data, some of which makes sense, but I'd imagine the majority of 3rd party tracker

It blows my mind how much of the internet economy is built on sucking up user data, some of which makes sense, but I'd imagine the majority of 3rd party tracker data is used for recommending ads. Ads a solid constituent of users ignore entirely. I have personally clicked on an ad in earnest maybe once or twice in my entire life. I know a lot of this data is poured into recommendation engines but it seems like those I use aggregate results mainly based on the product seller's contract with the site and anonymous user data. If you could observe the gross cost of aggregating all of my data would the net of purchases swayed by the results of tracker data aggregation exceed the cost if excluding purchases which would've been made without any intervention based on that data? I just don't understand the economics of, "data is the new oil" because it seems like the number of profitable conclusions that can be made on mass aggregation are limited to a small handful of huge companies, and those selling data snake oil to political campaigns or whatnot.