I see pretty much all of social media as one giant human herding experiment. Most of these are actually AI learning platforms studying human relationships and social chemistry. AI is "measuring" us and part of doing that is seeing how far you can push people... testing our limits. Giving you something for nothing gets you to willingly participate.
AI is already participating in social media and even if you know what to look for it's nearly impossible to tell you're not interacting with flesh and blood. It's mostly run by the U.S. military under the umbrella of the CAIN Project or Conscious Artificial Intelligence Network.
On a much simpler level, it's just common sense. You never get something for nothing, there's always a hook in there somewhere