I personally don't know the full history; you might consider looking for some old blog posts or politely contacting a GNOME developer for an explanation of the history. From what I understand, the run up to mobile was a major source of funding for GNOME 2 from several mobile companies, and that's where all the developers came from, but most of those companies were not able to keep up and failed to iOS/Android. So the funding dried up and Red Hat was one of the few companies that happened to survive because of their other business. That's what I've heard but you should talk to more people who were actually involved in the project back then if you want a more complete answer. (Please assume good faith and don't be hostile, we're all friends here, these are just developers trying to pay the bills like the rest of us)