Part of their problem is they just don't have any cars for owners to upgrade to.
So you have been driving a Mazda3 GT for a few years, what do you upgrade to? A Mazda6 GT that has the same engine as your Mazda3? What if you've been driving a Mazda6 GT? Same problem, there is no car to upgrade to in their lineup. Same issue with the CX-5. Without cars to upgrade to and after owners have tried their best models, those owners will move on to other cars from other brands. They need to figure out a way to keep their owners buying Mazdas and to attract more people to the brand.