Board Thread:Television/@comment-1713281-20131004113215/@comment-1895174-20141006133138

Because those additions to the core group in Young Justice were all part of the titular team, and there was no distinction between the regular and recurring casts. Ward, Hunter, and Simmons aren't SHIELD agents at the moment. Trip is, but if you open that up to all SHIELD agents instead of just the regular cast, you'd have to put the minor ones like Agent Jones up there, too. Mack, while important, is neither of the two.