Best 12:
I think in the 1950s the Shuberts had to divest themselves of many theatres under an anti-trust order from the US Dept of Justice. They operated under this anti-trust order until the early 1980s. Any new theatres they acquired during this time had to have an individual okay from the DOJ. The two that I know they gained were the Shubert in LA (now defunct) and the long term lease on the National in DC.
This also explains why there were non-Shubert-owned Shubert Theatres in New Haven, Philly (now the Merriam) and DC (torn down). The Shuberts also sold or gave up the leases on the Shubert (now Lasalle I think) and Blackstone in Chicago and the Shubert in Cincinnati was torn down and the land sold.
The Shuberts in NY were limited to the 17 1/2 theatres (now 19 with buying the other half of the Music Box + the Little Shubert) they own now.
There is a biography of the Shubert brothers and their company called "The Boys From Syracuse" that will tell you all this and more.
This ruling was lifted in maybe 83 or 84 and the Shuberts were thought to have the inside track to get what is now the Marquis. For some reason they passed.
"If my life weren't funny, it would just be true. And that would be unacceptable."
--Carrie Fisher