Facebook Platform, as conceived, was just a bad idea anyway. Zuck nailed it when he said that "today social networks are closed systems" but here's the kicker - Platform didn't really do anything to change that. They wanted people to build apps to run inside of Facebook, not to communicate with Facebook. They weren't ever tearing down the garden walls, they were asking everybody else to move into the garden with them. And most people didn't and the people who did (mostly) realized that it was a mistake.

I think they finally moved on from that a bit, but the "let's run an app inside a social network" thing was always of very limited value.