I think i read somewhere that the writers didn't know how to handle Rowlf like the did with Fozzie or Gonzo, so I think they stook him in those UK sgements so he could play his piano. I don't know if he became a vary big character like others like Fozzie, Piggy, or Scooter here in the U.S.
He could have been a major character if he interacted with Kermit. Actually he still could have been a major character if he was in the backstage a lot with other muppets like Piggy or Scooter, whn Kermit wasn't there.
Just for the record, Rowlf is my favorite character. I think he's better than Kermit!
ryan