Or the designers didn't think it was wise it to include a bunch of high-level monsters when the rules for characters only went up to 3rd level (At least in 1983 version, I never had the '81). I think dragons only made the cut because they were in the name of the game.Though as all of these were in the original boxed set and '77 Basic, but not included in '81 or '83 Basic , that still suggests the designers saw them as less essential.