Why do you subtract cash in the enterprise value formula?

Cash gets subtracted when calculating Enterprise Value because (1) cash is considered a non-operating asset AND (2) cash is already implicitly accounted for within equity value.  Note that when we subtract cash, to be precise, we should say excess cash.  However, we will typically make the assumption that a company’s cash balance (including cash equivalents such as marketable securities or short-term investments) equals excess cash.