Yes I'm sure all the 16mm lower quality inserts they had to use on the DVD is the reason this hasn't been released in HD. Probably a very expensive project since it involves the majority of episodes.
True and since they tried classic TV on Blu Ray with the 1st two seasons of I love Lucy, 1st season of Andy Griffith and The Honeymooners and those didn't sell well even at the bargain prices I think they are done with classic TV on Blu Ray. With the huge remastering cost that would be needed...