I think dismissing it as "political theater" simplifies the cause and effect, and the legislative process. Congress was controlled by Republicans in Obama's last term, but the popular belief was that not only would Clinton win in a dominating fashion, but the effects of her dominance would propagate downballot and win the Senate for Democrats, and at least make the House much closer. If that had happened, TPP would seem pretty likely to pass Congress in some form or other. At the very least, there would be more negotiations. Negotiations began back in 2008; Congressional reluctance was unlikely to kill TPP. Trump outright abandoning the plan will kill it more decisively.
Yeah, and it's great theatre! It's ultimately meaningless, but it does reinforce the story that Trump and the Republicans are trying to tell.
I live in Canada, and the politician who negotiated on behalf of my country is in the neighbouring city. At some point I hope to have a chance to ask him face-to-face how he justified negotiating that deal in secret.