I would guess just so that the gain of each stage can be tweaked easily. Since the balc voltages will be 4.2, 8.4, 12.6 you need a different gain for each the opamps such that each balance tap can map nicely to the 0-5V input of the micro.
Easy to just leave the footprint on the pcb and put a 0 ohm jumper if you don't need it.