The very best explanation I have ever heard comes from the famous Steve Ashton. Steve makes kilts and traditional kilt socks. He recreates patterns that are no longer made today in modern mills and like days of old he makes the socks custom fit to each customer. His experience and his willingness to share his knowledge is well known in the Circular Sock Machine world.
Steve said on Facebook that the answer to this mysterious question is:
The cause of “Dog Ears” in a toe is that the line of grafting, The Kitchener, adds one more line of knitting to the toe. To account for the Kitchener line we omit the last row of machine knitting and allow the kitchener line to replace it. So – when making toes you end on the left side and do not continue back to the right where you started. The Kitchener then grafts the toe closed from left to right.