I know someone who was is in the business, very high paid employee, like ridiculous pay. Perfectly legal, he is a data engineer.
They package all this personal information cultivated from a whole range of sources, put them in a nice neat package and much like mortgage companies package mortgages sell the packages to the highest bidders.
People agree to the "terms and conditions" of almost everything they download and buy.
It's kind of why I am a bit crazy about my posts in this forum with privacy.
It's really crazy and this is big money, just think about it. Let's say the loss Facebook faced of up to TEN BILLION dollars a year in revenue just by Apple tweaking a privacy setting not allowing cross site tracking among apps and tracking once the app is closed. (this is jsut an example of how much money is in the business with just one company in the whole world)