The original orbits would take ~100 years to decay, which is way longer than the life of the satellite. The new orbit is around 5 years (not taking into account maneuvers from the fuel on board). Makes a lot of sense, especially since it looks like they'll be iterating the design as they go (two that jumped out at me: initially not all satellites will be taking advantage of both Ku and Ka bands, and not all satellites will have phased array antennas)
Maybe using the ones in lower orbit to cover more densely populated locations?