The latter; members did not sign up for it in sufficient numbers.
Right... and my guess is that none of them cited parking as the reason.
I agree, it's a pain in the butt, but it certainly isn't "The End of Days" as some would lead us to believe. It isn't even the "End of Tobermory" as the OP has prognosticated.
The reality is that tourism in Tobermory has never been stronger. With the US dollar strong again, there are lots of US plates in town... There are busloads of Chinese and European tourists arriving daily. Tourism is so strong there currently that I have been "threatened" on my FaceBook page for posting images that supposedly are attracting tourists, but to the chagrin of locals (Who are neither local by birth or even residency... they're mostly ex-pat bird watchers from Toronto).
As I mentioned earlier, of divers stop coming to Tobermory, they will ultimately be the ones who suffer since the shops will close, the charters with stop and that'll be it.
In fact even now, many divers show up with all of their tanks for the weekend because they don't want to pay Tobermory fill prices... Easy for me to say I know, but still, supporting the locals is never going to be a bad thing, although divers as a full tend to be a frugal bunch...