The sub market is pretty crowded, so they may not want to get too complex a product line to avoid additional confusion (much like they are keeping their new speaker line pretty simple). For that matter, passive subs have largely faded from the marketplace - HSU no longer offers any, and the only passive SVS's are the cylinders (developed when SVS was new and they hadn't developed a way to mount a plate amp in a cylinder). The powered sub has become something of a staple of home theater, with passive subs being much more rare.