Comment by nostrademons

Do you do any ML for Big Tech? Because it's actually a lot simpler than that: the input is the sum total of your activity, and the output is the likelihood that you'll click on an ad or buy a product on a specific surface. You certainly can predict demographic information like sexual orientation, education level, income, political party, and with a fair degree of accuracy, but all it does is add noise to the calculation you really want, which is optimizing the amount of money you'll make. To the extent that demographics are computed, it's to make advertisers feel better about themselves. They would almost always be better off with a blanket "optimize my sales" campaign, but it's hard for ad agencies and digital marketers to justify their existence that way.