The issue is that even though there are better coins for privacy/speed/etc, none of those dev teams are reaching out to create partnerships in the legal cannabis industry. You have to remember that the vast majority of the population doesn't really know what cryptocurrency is, let alone how to use it. So the teams behind a number of these marijuana coins have been putting in a lot of time to bring their crypto to the businesses rather than waiting for businesses to come to them. Maybe one day those businesses will look deeper and decide to go with BTC or DASH or whatever, but for now most of them are probably only willing to give it a shot with dev teams that actually communicate with them directly.