Couldn't they still pay extra and get it? Can't you do that in Canada?

Nope! Physicians either have to be a part of the public system 100% or 0%. No doing both.

As a result, there are very few private options for healthcare in Canada.

A family member of mine is an orthopedic surgeon in Vancouver. Several years ago he split his time between a teaching hospital and a private practice, doing knee surgeries at both. At the hospital waiting times were typical. At his private practice waiting times were very short, on the order of days, I think. IIRC, the way surgeons get around the rules is by charging by the hour, not by the procedure. And it's completely out-of-pocket. For the kind of cookie-cutter, out-patient operations he specialized in it worked very well for him and his well-heeled patients.

Right. As I mentioned in my post, there is a concern that allowing otherwise would erode the public system. Perhaps it's justified; I don't know. Also, those who can afford it can travel to the US or elsewhere if they want to pay for services, which reduces the motivation to create a private alternative here, although it turns out in practice that happens rarely. This is a good overview, also covering the differences in wait times between the systems: https://motherboard.vice.com/en_us/article/fact-checking-tru...