Once upon a time I did competitive ball room dancing and cha cha was, and still is, my favorite. Hines is not bad but I do agree with the judges. He's not smooth enough. He is too stiff in the hips and his footwork was off. His posture was badly off as well. You have to be on the balls of your feet and he leaned forward far to much which threw off his balance and made him clumsy. He was also understandably nervous and it showed particularly when he was not dancing close to his partner. Most importantly, in ballroom dance the man leads, and the woman follows. Hines wasn't leading.
If you really want to see how it should be done watch a real dance sport competition on your local PBS station. If you can catch the world championship or you can check this out.