But maybe I'm missing something obvious.
This lines up with my experience. I did a ton of (painful) Facebook platform development from 2007-2009 or so, but I haven't followed it as closely since. My sense back then was that there was this huge build-up of activity around the FB platform; they were creating all these new APIs and ways for developers to build super social experiences and deeply integrate with the core FB experience, there were huge companies like Zynga that were entirely dependent on Facebook and also were responsible for tons of FB revenue, etc. And then it all seemed to fizzle? It doesn't seem like there's really hardly any activity any more in terms of deep integration with Facebook as a platform, other than FB login. I never see anything on my news feed any more from weird apps, or get invites to take some dumb quiz, or whatever. I mean, I'm sure that stuff is there somewhere, but not anything like it was. That could be wrong though!