It occurred to me that there may be a generational thing going on with the survey structure.

Mudcat, TheSession, BanjoHangout and their like are much older than general-purpose "social media". To a Mudcat old-stager, Facebook is the same sort of thing as Mudcat, only with a wider remit and different strengths and weaknesses. It doesn't make sense, for us, to think of them as requiring different sections of a questionnaire. But for somebody whose first exposure to any kind of computer-mediated interaction with their peers was through services like Twitter and Facebook, going to a dedicated music forum is odd behaviour that needs explanation.