What say you, monks?
Asking those that are still here will probably not elicit good explanations.
Is it possible to go straight to the horses mouth and ask former active members to say why they are no longer such? Anonymously or otherwise. Perhaps those here that are still in contact could email them to ask them to post a short explanation of their reasons for moving on.
Perhaps it could be wrapped up in a poll? (It'd be nice to see a useful one for a change :).