When I saw Murphy, the theater was packed... but I got my ticket either through TDF or through a discount on Today Tix, so she definitely wasn't pulling in the money that Midler did.
And crucially, she was only doing one night a week, bringing in extra income when the star wouldn't perform (bearing in mind that the cast and crew are paid by week, not by number of shows), and minimizing the rate that the production would go through the fans who wanted to see her in the role; if she sold out eight performances, that was two months as compared to one week, and as long as she pulled in more money than it cost to run that single performance, she made the production a profit, because they would have otherwise been dark.
For that model to work, the show would have needed to find both another mega-star like Midler and another Broadway star who would have been happy being a glorified alternate, and who fits that bill? I doubt Bernadette or Buckley would want that gig, and I doubt that Carolee would have quite the same draw as Donna Murphy. There are a few names that spring to mind, but that's a very hard circle to square.