I believe the issue with seeing it on DVD is much the same as other licensing issues. As far as I know, someone in the way of Ed Sullivan's family or company or something owns the special as a whole, yet Disney would own the rights to many of the early characters. Yet at the same time, I don't know the exact details of the JHC to Disney transfer, but I wouldn't be surprised if JHC still owns the rights to some of the characters in the special that were unused otherwise (i.e. Thig).