Do you think they’re trying to monopolise user data to sell to advertisers?
It's the biggest one, followed by company specific recommendation engines.
Usage stats could help you improve a user interface, teach users new skills (eg: "you always do this, here's a shortcut to save you time"), perhaps more personalized operating system interfaces and defaults.
You probably don't need a fancy pseudo "AI" system for any of these, but that's the current gold rush so someone's gonna do it