Waaaaay too many DVD singles and sets that were cancelled in favor of newer sets and so on.
The only DVDs that never got released were the final 3-4 volumes of "Season 2." Every other episode was released via the singles. And FUNi wouldn't have bothered with the Orange Boxes (at least, not that early) if the singles were selling. And considering they haven't been re-released in a slimmer package yet shows that they still are.