Even if the CX-9 had come along with the most space in class, most features in class, most power in class, while maintaining the best styling and driving dynamics, it would still be one of the slowest selling models. Brand recognition, past reputation, dealer network, all play as big a role in sales as the product itself. Sadly. People go shopping for a 3-row and Mazda doesn't even enter the buying process for most people. Just the way it is. What do you think would happen if they introduced the best full-size pickup on the market, even with a V-8? Nobody would buy it. Simply because it was a Mazda.
The best cars in a segment rarely are the best sellers. Just go check out all the best sellers. The Explorer is actually the worse vehicle in this segment (mostly due to its age), and it's the best seller. The CX-9 has won almost all comparisons, and it's the least selling model.