Why do you think so many smartphone apps are free. All they require from you is your attention! Why do you think Steemit incentivizes the attention? Because the more time you spend somewhere, the more value you place on it.
Free apps use all of your personal information that you freely give them to sell your usage patterns to eager corporations. That's why they keep bugging you to spend more time on them. It's a terrible thing.
Yes, and they have well-paid teams of behavioural experts to help them engage us. Watch out. ;)