To put it as succinctly as possible: Disney's product research/development department is clueless. Especially when it comes to the Disney Store end of things.
For the latest example, I point towards the Princess Designer doll fiasco of late August-Oct. 17th of this year. Really nice collectible dolls, mugs, clothes, etc. for ADULTS. Sadly adult merch is something they have very much run away from in the stores, with the excuse that it doesn't sell. Absolute chaos ensued for that entire line because Disney did not believe there would be much of a demand for any of it and didn't make enough of most of it.
The Muppets, sadly, are no different. Someone in the bean counting department thinks that stuff like G-Force is a profit machine waiting to happen, but they thus far do not see the potential with the Muppets. Sad. I hope that will change, but then again, they still haven't been able to buy a clue and realize that there is a huge demand for Tangled merch, and not so much for Princess and the Frog merch.
When Ulta (a makeup store/salon in the U.S.) has a huge display for the OPI Muppets nail polish right when you walk in the door, but the Disney Stores have their Muppets "display" in the back, that alone shows the sad state of affairs at the WDC. (The OPI polish has been a MASSIVE hit around here, btw; almost an instantaneous sell out each time a truck comes in.)