There are two reasons for that.
First, the Régie de l'assurance maladie du Québec card does not cover dental care for the vast majority of Quebecers.
Second, 95% of providers in Quebec are registered with the Canadian plan. Sun Life is working very effectively to get dentists, denturists and hygienists paid quickly, in less than two days, and to make it simple for them to provide customer support. They took on vulnerable patients who would not otherwise have gone to them.