They own the data. It is their ball and they can basically say "I'm taking my ball and going home".

Facebook, twitter, linkedin, google. All of them are in the data business and sell that data to make a profit. They don't really care about the devs as they just see the devs as a way to bring people to their ecosystem; the more small apps people write, the more ways they might be able to get data. But, if they get big enough, and all of them have, they can cut you out.

I understand building a business around someone else's data (cottage industry), and I would never say not to do it, but it isn't without peril. Though, I would do it in a heartbeat for a lifestyle business that I knew I could pivot on or build another if it failed.