I would imagine the problem is that all the stars mentioned are based in the L.A. area. That means no one has to pay to get them to the show. If the show was held in the N.Y. area, they would either have to bring those stars to NY....or showcase NY stars.
When you think about it, the situation in New York is very different. You know exactly where to find the performers. If you want autographs of Broadway stars, all you have to do is buy a ticket to the show, and be prepared to wait at the stage door when it's over. They are, for the most part, very happy to spend time with the fans. My daughter's collection of autographed Playbills is turning into a paper tower.