Other mistake: During "Cool," there's a shot where they're doing a sort of knee turn, and you can see Tucker Smith in the background spinning too many times (you can see him start to stick out his arms to stop himself). (01:58:20)
Other mistake: When Anita sings, "and the natives steaming" her fingers get caught in the fringe of her dress. (00:50:05)
Other mistake: In the prologue, after Riff stands up and signals to the other Jets to follow him, they all stand up, then in the next shot you can see Baby John stand up again.
Other mistake: During "Cool," Baby John spins around and when he stops with his arms spread out, his right foot stumbles a little. (01:58:15)
Other mistake: During the dance at the gym, Maria doesn't snap each time she should have. Natalie Wood was unable to snap, so it was dubbed (as well as her singing, which was dubbed by Marni Nixon).
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