While I agree with your argument that the body does not maintain one specific pH; each part of the body needs it's fluid at a certain pH to function optimally. However, couldn't some fluids in our body be over acidic or over alkaline?
Blood is really sensitive so we won't talk about that. But what about fluids in the lymphatic system? Could it be that the lymphatic system is functioning poorly according to an individuals body composition such that the fluids/regions become over-acidic? Since the lymphatic system has to remove cellular waste products, couldn't a certain area become over acidic because it isn't able to be removed effectively? It could be due to weak kidneys, a sedentary lifestyle, poor diets causing too much inflammation, etc.