First time it happens for 2 reasons.
1) while out of the 2 book movies (at the time) MTI was my favorite, Piggy seemed tacked on as a contractual obligation. Almost like she said, "Listen frog, I'm I'm not in the movie, you're gonna be sleeping with those fishes!"
"But you don't fit into the script anywhere... maybe... maybe we can make you a pirate wench"
"PIRATE WENCH? HIIIIIIIIII-YAH!"
2) Joe Raposo. One of the few time he wrote for the Muppet Show Muppets specifically. WHihc is great. I almost wish he worked on Fraggle Rock as well.