Revealing mistake: The knives at the rumble bend EVERY time they move.
Revealing mistake: In the final scene, if you look in the background that is completely opposite of the gate where the characters exit, there are two cars obviously made of cardboard. Many times they can be seen by looking over Maria's shoulder. (02:22:05 - 02:25:35)
Revealing mistake: When Maria is cradling the dead Tony you can see Tony's chest heave as the actor takes a breath.
Revealing mistake: In the dance scene, when the two gangs are "battling," if you look in the background at the Sharks side, you can see Maria among others mouthing the rhythms of the songs. (00:37:25)
Answer: People would not come to the theater to see Marnie Nixon despite the fact that she has sung the lead roles in West Side Story, The King and I, and My Fair Lady. They'd rather see that darling girl from "Miracle on 34th Street" again (or Deborah Kerr or Audrey Hepburn) than an unknown with actual talent.
Myridon