they did, but i didn't mind. it showed that the characters' lives continued after the ending of the show, and everything didn't up neat and packaged with a little bow on top. it added a sense of realism to it. also, from a fandom point of view, it's kept people speculating about it long after the show ended. it would definitely be nice to know what happened to everyone from the original show, but to make a new series just to tie up the end of the series would, again, be overkill. personally, the only resolution i'd like to see would be with zuko's mom. and the return of space sword and boomerang, of course
anyway, turns out korra's going to be a mini-series with about 12 episodes. there's apparently also a character named meelo.