Filmation closed shop and, supposedly, was sold to the French division of L'Oreal, yes, the makeup company. (Don't ask me the logic behind all that!) Thus, the ownership of the material exclusive to the animated series (M'Ress, Arex, Vulcan "mountain lions", etc.) was in question. It was safer just to avoid including those elements in any "primary" production (TV series, movies, etc.) until the issue was resolved. It didn't help the cartoon's cause when Roddenberry started disavowing certain materials and his PA Richard Arnold took advantage of his position to "disown" it as he personally did not like the animated adaptation.