An interesting point Molehill. There's the thread about the list of those who've completed the classic big three (or national big three if you prefer). I think the successful completions are roughly 1900 for the BGR; 100 for the PBR and 70 for the CRR. Obviously the BG has been established for a lot longer but even so - there aren't 140 attempts on the PBR or CRR each year.

The CRR I can understand as it's not close to most people but the PBR is probably no further to get to or train for than the BGR. Maybe folk get the BG done and think "can I go back to short races now?" I had a go at the PBR but got nowhere.

I'm fortunate in that I live in the country so can just get out and go wherever the mood takes me (these days it's biking rather than running but the ethos is the same) but if you live in a town or city then that's not much of an option. I don't think you can mandate what people do: some (most?) will be happy to run the familiar trails or races, it will only ever be a small minority who just head out on a day long run that they've thought up the night before.