NEMA patterns aren't that old...dating maybe from the late '60's. Nor does every industry care about NEMA protocols. The RV industry being a case in point- RV manufacturers typically had little contact with the electrical community until recently, and developed their own standard.
Perhaps the real question should be: Was NEMA showing its' own ignorance when they ignored an existing pattern when they developed theirs'? This is not the only such example.