Just on a competitive level - i don't know why Palisades prices themselves out of the market a lot of the time, when these things are on the shelves they are placed next to cheaper products from more popular brands so even if the other stuff isn't so good looking it still has the advantage over the Muppets.
You just answered your own question. They are cheaper BECAUSE they are more popular. At an already expected lower volume, you just can't go in at a lower price. The Muppets do not have the brand recognition you may believe they do. These are comparably priced with other niche collectible PVC sets though, the smaller brand ones you'd find in comic shops. If this were Star Wars PVC, or Looney Tunes even...well, then the volumes could be projected and believed in so they could be $15 for a pack of 6 at the very start of it. Bottom line? We already know going in that the volumes will be weaker, so they have to be priced accordingly.
I love the PVC's - but they've had time to get to know the Muppet market now, if they expect to sell lots of these (especially with some fairly obscure characters), they're completely bonkers !
We don't expect to sell a ton of these...that's why the price HAS to be higher than a higher profile set. That's the way it's gotta be. Is it possible we would sell more at retail if they were cheaper? Maybe...but there is no evidence to support that theory. It's brand recognition...plain and simple.