Well I'm sure it has to do with Jack's idea of art. I mean, Rerabrandt doesn't interact with you when you look at his works. Nor does Michaelangelo, Stravinsky, or Keats. I think to Jack, people are there to take in the art and too much stage presence would be (in his mind) self-glorifying. We're also talking about a man who could care less for the press. I think part of him shies away from coming off like artists he might feel aren't really artists.
This is no attack man, im just spinning it in perspective. When i saw them, he was the same. I felt it was par for the course.