Short answer can be summarized as follows: Can X correlate data "that way" about users at scale and at an acceptable cost? If yes, then X does it. Works for al

Short answer can be summarized as follows: Can X correlate data "that way" about users at scale and at an acceptable cost? If yes, then X does it. Works for all companies that generate revenue from targeted advertising (GAFAMs of course, and many many others).