Also there is the simple fact that a lot of the time the liquid spilled is rather small, with most liquids tracking in units of about 1 cup (some, like alcohol, gasoline, or mutagen are much smaller). For an example of how this may be difficult to do, get yourself a cup of water, now pour it on the floor (or on the dirt, concrete, whatever). Now see how much of that liquid you could actually retrieve with a towel or mop, then ask yourself if you would actually want to drink any such liquids retrieved in such a method.
Of course the idea breaks down when dealing with things like pouring a whole 50-gallon barrel on the ground, but there are a lot more times when a person spills 1-2 units of liquid then any significant amount.
