I don’t know if it is the reason why the port was put on the bottom originally, but I can think of one reason why Apple didn’t decide to put the port on the front in this new mouse. Have you looked at the front edge of that mouse? It’s very thin. The front edge that the mouse is only a few millimeters above the desk surface. Also the optical sensors are very near that edge. I think, if Apple were to reengineer it to allow for a front port, they would have had to completely redesign the mouse and they clearly didn’t want to do that at this time. Even if they were to use one of the other sides, it wouldn’t work. The back also doesn’t have room, and the sides are where your fingers grip the mouse and a port there wouldn’t feel good. I think they took at look at it and decide the belly of the beast was the best place for now.