I think he is, of course, just trying to stay away from the train wreck that was the film. I think he would not have wanted any kind of involvement with a Cats film (besides remotely writing one song) because he is smart enough to know that it was very likely to be terrible. There was a lot less to work with than the Evita and Phantom films, and they were hardly unmitigated triumphs.
Because of the nature of the material, it would be hard to make it into a film. The narrative is barely there. If it were to be made as an animated film, you would lose the choreography. In fact. If it can be enjoyed at all, it is as a dance piece, punctuated with a few nice but disconnected songs. Not the parts with which to build a conventional coherent movie. Plus, yes, the visuals in the film were creepy.