Maybe in the SUV form, there isn't a need for leaf springs. It sure keeps the costs down, while providing the same ride, if not a better one. It has worked remarkably well. Many reviewers have stated this is the best riding, leaf spring suspension truck on the market. Some even stated, having an equal, if not better, ride to the coil sprung SUVs.
Engineering is the name of the game.
To get the best performance, with the least amount of bucks. Anyone can design an expensive coil system, but it will have a higher cost. It may not have any significant improvements over a well engineered, lower cost design. I really don't see that happening myself. That's why there's the expensive Pathfinder.