Probably for three big reasons.
1) U.S.S. Yorktown was known for having been sank by the Japanese at the Battle of Midway while Enterprise survived the battle and survived the war as the most decorated U.S. ship.
2) The first (and at that time only) nuclear powered aircraft in the world was the U.S.S. Enterprise and had made a number of very high profile deployments.
3) As stated above, "Yorktown" was overally Americancentric being named after the penultimate battle of the U.S. Revolutionary War. And it is even possible that G.R. even then was contemplating overseas marketing.