Why is The Law of Conservation of Matter a law and not a theory? will brainlist

During a chemical reaction, matter cannot be created nor destroyed, matter can change form through physical and chemical changes, but through any of these changes, matter is conserved; even though the matter may change from one form to another, the same number of atoms exists before and after the change takes place. <3

It's not the same dearthe first one is in grams per mole while the other is not