I think you are correct here. As illustration, Colorado 2012, the legalization of cannabis united more, and got more votes (by over 50k) than Obama did, who Colorado voters loved. Party affiliation never entered the picture, and had no part in the #64 movement. In fact, we had LEAP (Law Enforcement Against Prohibition) on our side, an anti-prohibition org with over 100K members formed by about 6 cops.
However, the most influential public person on #64 was probably Mason Tvert, who began his fight for legalization way back when he was in college. And the legalization legislation battle actually began back pre-2000, and Amendment #20, medical marijuana was voted in 2000. It took 10 years to implement. #64 only took 2 years.
I think the 15$ movement has the chance, but it needs to form with other issues to be massive enough. That is the trick. BLM, LGBT, Immigration rights, equal pay, climate change The passion of Occupy with the number of people of the Tea Party.