There is a reason: Firesale!!! Bitmain is practically being run out of China, by their restrictions and regulations. Rather than paying to relocate all of their miners, they mine with by the way, they'll sell them off. Also, I'm sure they are looking for funds for their next gen hardware. As for the appearance of more efficiency, it's simply marketing. The implied efficiency, is still within the specs of their original equipment. They just slapped an "i" on it.