From the Times article:
“Twenty years is a good run,” Mr. Viertel said. “I came to the artistic directorship with a very specific bucket list of shows that I was fascinated by, and actually that bucket is empty.”
With producing a series like Encores, your bucket list is pretty much taken care of once you've uncovered such lost gems as Pajama Game, Hair and Bye Bye Birdie. It seems everyone is doing those shows these days.