Why are cats said to love milk?

I don't know but my cat isn't to keen, i buy him cat milk and when i open it and give him some he will drink it so the next day give him some more because it need to be used within 4 days and he won't touch it. So now when i buy any i give him some and the rest i freeze in ice cube treys and give him a couple of cubes about once a month as a treat. But he doesn't like it very often only when he hasn't had any for a while.