In the course of Hollywood history, movie genres have grown from the the lower regions, among the ticket buyers and popcorn munchers, in the Saturday matinees and with the dime store, penny-a-word trash classics. The Western was the first of these, making its movie debut as early as the movies themselves, with The Great Train Robbery (1903). Not fifty years had gone by before some wise guy had the idea to take this ground-level idea and turn it into an impressive, blue-ribbon pageant, a noble, tasteful new object worthy of respect. These came in the form of High Noon (1952) and Shane (1953), praised through word of mouth, as Westerns for people who don't ordinarily like Westerns. Critics ate them up. And, if you'll notice, the Western genre is more or less gone.
The same thing happened to musicals. As soon as pictures learned to talk and all through the 1950s, musicals ruled, and plenty of great, small ones crooned and tapped their way across screens, much to the unfettered joy of fans. But in the 1960s, the graceless, inflated, gargantuan West Side Story (1961) -- a musical for people who don't ordinarily like musicals -- came along. And now the musical is more or less gone (and, I'm sorry, but Dreamgirls doesn't count).