Because then he’d have to admit they were in combat, and ‘boots were on the ground’.
Via Townhall:
Tuesday morning Defense Secretary Ash Carter announced a Navy SEAL operating as an advisor to Peshmerga forces was killed on the front lines against ISIS. Carter specifically said the SEAL was killed in combat after he was shot when ISIS soldiers broke through an Iraqi forces checkpoint and made their way to Peshmerga territory just outside of Mosul.
Despite the classification by Carter that the casualty was in fact a combat death, the White House is still refusing classify the role of U.S. troops in Iraq as combat. Since 2014, three U.S. service members have been killed in the war against ISIS.