Just style - with a QD wheel arrangement, the chain & sprocket remain in place when the wheel is removed. Another carry-over of the "race bikes for the road" sales culture - race bikes don't have FERCs, so your road bike doesn't "need" one either.
Another example of the sacrifice of practicality on the alter of style - along with functional mudguards. My NC750S is, in many ways, the most technically accomplished motorcycle I have owned. It is also cursed with the most ineffective mud & chain guards of any motorycle I have owned. Progress, hmmm ?