Presentation, how to describe it. For me it begins with posture, on and off the floor. If you watch championship dancers you will see that they literally exude confidence with their upright posture and fluid motion as they walk. Once on the dance floor they add frame and expression. Their necks will seem long, their shoulders will be down and they will assume their dance position deliberately. This is all before you begin to dance. While getting this far won't win you any competitions the absence of a good start can assure you will not win.
Presenting yourselves well for a one minute and twenty seconds as you dance can seem like an eternity. The smile can disappear, the shoulders can rise, the frame can droop or compress and you can find yourselves unstable in a myriad of ways. These are all things judges can see before they even bother to check out your footwork or evaluate the complexity of your figures.
I am sure others may be able to offer a better or fuller explanation. Simply put, if you don't look great you are probably not dancing well either.