It's gone from being an SUV riding on a truck platform to a CUV/crossover, which rides on a car platform, so the design change makes sense. The reason for the change? Most people didn't off-road with the old Pathfinder (most people don't off-road with any SUV for that matter); the old boxy shape was not very aerodynamic, which harms fuel efficiency; and a car platform is an inherently lighter design, which also improves fuel efficiency, plus it offers better ride and handling. Nissan has just taken the same path as so many SUVs before it, like the Ford Explorer and the Chevy Traverse, which used to be truck-based, too.