I always had a hunch the DVDs didn't sell well, and this always seems to be an issue with Disney in general when selling TV shows on DVD.
Maybe if all the Muppet enthusiasts petitioned or got out a lot more, perhaps? If we just continue to sit in this forum complaining and ranting how they may never be released, it just seems nihilistic to me. I always have a little bit of optimism about such matters, even if it's been a long while.
Bear in mind that by the time TMS was personally cancelled by Jim Henson in 1981, it was one of the most popular shows in the world. The show exposed the Muppets into the TV mainstream. Fans everywhere were drawn to this cult phenomenon about a bunch of celebrities being with a bunch of wacky and upstaging puppets (in fact, some of them even wanted to fly to London to attend tapings since they THOUGHT it was videotaped in front of a live audience). And more importantly, it broke barriers on how we perceive puppetry today, since Jim tried to pitch the show to CBS and ABC but turned it down because of their perception of puppetry as only a children's art form. True, that was a generation before, and especially back when Jim was still alive, but look at what it has become. We have a Muppet Wiki, a Muppet forum, Muppet merchandise, Muppet media, Muppet this, Muppet that. Although it may be not as big as Marvel or Star Wars, I think we have a pretty good crowd out there that can plea to Disney numerously.
Again, like I said before, they've probably put both sets on hold because of copyright negotiations. Debbie McClellan has stated this, and she has also said that if we are serious we should get out more and encourage Disney to finally release them: send out petitions, e-mail them, phone their representatives, etc. Maybe if the momentum is strong enough, it will give them a sincere reason to release the remaining seasons.
If anyone wants to write a(nother) petition, I'm ALL for it. And even if
eventually (emphasis on) that means another viable third-party option like Shout! Factory, then let's ask them about it.