I think that it is because, from the meaning of chemistry, it is the study of matter, its composition, reactions, and etc. So when you talk about matter, you can say that it involves the whole universe starting from the sea, the beach, they are liquids: Chemistry, the air, the oxygen we breather: Chemistry, the things we used, pencils, erasers, solid: Chemistry! That is the reason on the explanation why chemistry is sometimes called as the central science.