There's a slew of reasons why someone would produce a show that won't turn a profit, especially as adamgreer said, if you can keep the people who make you money in other cases happy by doing it. I also imagine there's a whole deal of respect and sentiment for veterans like McNally, Rivera, John Kander, and Fred Ebb. Adamgreer, I think your mention of FOLLIES is a good example. This could also be a passion show for the producers, one they know won't make money but one they would be proud to be associated with. Either way, a new Kander & Ebb show starring Chita Rivera would be a welcome addition to any season.
"Some people can thrive and bloom living life in a living room, that's perfect for some people of one hundred and five. But I at least gotta try, when I think of all the sights that I gotta see, all the places I gotta play, all the things that I gotta be at"