Readers would, of course, be confused by 2 King Arthurs. I am, of course, being sarcastic. Most likely, the same reason Aquaman became a joke in Superfriends: Aquaman works best in the water; they probably didn't want to shoehorn a scene of him in the water just to justify his appearance. They only had, what, 20 pages? Or was this back when they allowed a couple more pages?