Because she's embarrassed. She's been pushing ARTPOP as unique, out-the-box and something that doesn't follow the typical 3:30 length of radio hits, when really it's as commercial as you can get.
I don't want Art Pop to happen. I love when everything is brand news to fans, she always reveals her stuff months/years before it's release to the point that there's nothing to look forward to but the music and even though that's what matters at the end of the day, guessing, thinking and getting exciting over the album title/album tracks is what's fun about the pre era of an artist.
OBVIOUSLY she's only just gotten to the point where she's well enough to do performances and stuff. Not to mention that she needs time to rehearse and learn choreography and stuff after she's healed.