There's also the fact that the black market is massive and deeply-embedded in American (and Canadian) society. Even without taxes it was never going to just disappear, certainly not in a single generation. Add to that the fact that most states still don't have legal weed, so wherever someone is growing they are not far from an illegal market. Plus, with use so widespread compared to every other drug, there exists a large enough youth market to keep a pretty big black market going indefinitely.