Well, the pigs aren't neccessarily my favorite characters. I have just noticed recently that hardly any Muppet pigs besides Piggy have been used in a long time. I guess it's possible that Link and Strangepork may have worn out (though I don't know for sure), but I would be surprised if all the other pig puppets have worn out by now.
Not to mention both Link and Strangepork need to be recast. I heard Steve plays Link now, but I've only heard he had a line in the Racemania game... and that was 10 years ago. But then again, we've basically had only movies (DTV's and telefilms, mostly) and none of them have ever had that big a role in film.
We did have Howard in VMX (who was rechristened as a new character in Tinsel Town), but that's about it. We also don't see enough generic, nameless pigs.
And I do feel it's a shame. Why, pigs are as much the Muppet Show as Chickens, Penguins, and monsters....