Plus, because they are unarticulated, they can be made in more dynamic poses that can't work with an action figure.
The best thing, though, is since they are cheaper and can be sold in a pack, it will allow for the inclusion of some lesser-known and obscure muppet figures for the fans. Also, it will allow for some theme sets with variations of regular figures that wouldn't work as well in an Action Figure line.
For example, recently the Simpsons line released two sets of themed mini-figs (similar to PVC, but articulated) based on episodes Deep Space Homer and Homer At Bat. The astronaut pack had Homer & Barney, but also had a Monkey, a NASA scientist, and Buzz Aldrin. I don't know many people lining up to buy a Simpsons version of a monkey or a NASA scientist, but put them all together in a themed pack and it works much better.
In other words, expect to see things like Penguins and other random Muppet figures that don't have enough strength to be sold on their own but add character to the Muppets in general.