It’s very hard to imagine what it takes to mount a Broadway musical if you are not involved in that world. It takes a long time, a whole lot of money, lots of patience, and many people. Commercial theater, anchored here in NYC by the 15 unions involved with it, is enjoyed by millions, but it is its own world.
In the process of putting together a show, many things have to happen before it gets into opening night shape. Along the way, actors are cast to do their thing, which in a musical means act, dance (usually) and sing. The singing may cover any kind of vocal production, so this ingredient varies quite a bit.
Those who do not tread the boards in a professional production do not comprehend how much  theater people live a life that cannot be found elsewhere. It is not found in small regional companies although something like it might be found in larger professional theaters. The “backstage mystique” that performers develop over years of being in many different kinds of shows is powerful. Opera has its own world, too, which is different. A few people manage to live in both worlds, but it is very difficult to go back and forth from Broadway to Lincoln Center on a regular basis successfully. They are only a few blocks away from each other, but it’s a long distance artistically speaking.
There have been many opera singers who retired from opera and went downtown to do a Broadway show, or maybe more than one. Ezio Pinza, Jan Peerce, Shirley Verrett, Spiro Malas……all did well on the Great White Way after they were no longer singing at the Met, but while on Broadway all of them also stayed in their original “operatic” vocal production. No one has gone the other way, from Broadway to the Met, nor are they likely to. There were rumors about Audra MacDonald and Kristen Chenoweth going but so far that hasn’t happened. We have seen Paulo Szot making the journey to music theater in South Pacific, and he is expected to return to opera (or perhaps has already), so perhaps he will establish a new cross-over trend. He is someone, however, who sang in the most legit of legit shows and did not need to change his vocal production one bit, in keeping with his older, earlier peers, so he isn’t exactly “crossing over”, he’s just crossing the street and going down the block!
If it were easy to sing really well in a completely classical sound and also turn around and sing in a variety of other sounds and do an equally good job, more people would have done so all along. Clearly, it requires a very special set of vocal skills to change gears in this way and most people either don’t have them, don’t want them, or don’t know there are skills to acquire in the first place. The “legit” singers on Broadway were the classical folks and there is almost no true legit singing left, even in the legit shows that are revived. The sound, on Broadway, is nearly dead except in revivals like South Pacific, where the sound is an integral part of the character.
Producers, of course want to have successful shows that make money. Given that the odds for doing a Broadway show are abysmal (75% of shows fail to recover their initial investment), they are always looking for something that will capture the audience’s interest and enthusiasm, and these days, with audiences being largely ignorant of both music and theater, the flashier the show, the better the chances it will succeed, even if it doesn’t have much going for it in the triple threat department. Spiderman got uniformly awful reviews but the show is doing well. It cost over $65 million dollars to mount (think about that, $65 million dollars!!!) and caused two very public law suits but people are going and it is making money every week. There are no stars, there are no really great voices or dancers. The cast is interchangeable, mostly unknown and mostly young. So why do the audiences go? Because they all know the character Spiderman from the comics and the movies and they have heard about the technology — the real star of the show, despite its dangers to the actors. It will probably run for a very long time.
The older shows, or ones that are written to be like older shows, don’t last nearly as long. The plain vanilla of great acting, wonderful singing and a good story brought to life by excellent actors pales in comparison to a huge set with flying people. And, in a society that values violence as much as ours does, saying that a show is “old fashioned” (sans violence) would strike many people as a strong condemnation.
The real world of Broadway isn’t something that you can read about in a book or a blog and understand. It is itself, unique in the world of entertainment. It has its own rules, folklore, expectations and weaknesses. The real world of music theater on Broadway is very small. The people who inhabit it live a special life and understand that the essence is not something that can be taught or written about, but has to be lived.