Answer:
Because No New Substance if Formed!
Step-by-step explanation:
When ice melts, it is still considered to be water, it's just no longer a solid. The molecules of water do not become something else and simply just change phases. A chemical reaction requires that a new substance be formed, for example when you burn paper, a new substance is formed. Also melting ice is reversible, you can just freeze it again, while chemical reactions cannot be reversed!