I suppose I'm only reiterating points other people have already made, but nonetheless...
Danielle and Jade have ongoing celeb careers whereas Jo doesn't for two main reasons.
Firstly, Jade and Danielle were savvy enough to realise that an apology was going to be required from them, and they delivered it. In my opinion, their apologies were insincere, but they paid lip service at any rate. Jo foolishly never apologised. This was, in a way, honest, but unfortunately it did make her look bad by comparison.
Secondly, Jade and Danielle (and especially Jade) didn't get their careers back on a plate. It took a lot of relentless publicity-seeking, trying to get in the paper for anything, no matter how sordid (Jack supplying much of the sordidness in Jade's case). The sheer shameless brass neck involved must have been considerable, but Jade and Danielle apparently have that in spades, along with a hunger for fame that made it impossible for them to contemplate returning to obscurity. To them, even being hate figures may have seemed better than being ignored.
Jo has, I think, a different kind of personality, much weaker than those of the other two. She couldn't have marched off out clubbing as if nothing had happened, like Danielle did. For Jo, I think she had to be either a well-liked celeb (as she had been in S Club) or retreat from celebrity altogether. When her interviews trying to win the public's pity largely failed, she chose the second option, and she hasn't so far as I know been anywhere in the media for many months now.
Bear in mind too that Jo's career as a singer is a bit different from Danielle's career as a model and Jade's career as whatever Jade's career is supposed to be. Danielle can do a photoshoot, or Jade can get papped by the tabloids, without caring what the public think of them. But for Jo to stand up in front of a potentially hostile crowd and sing would require a lot of nerve. As much as I wish Jo well, I don't think she's ready to do that.