A buddy of mine back then said that MTV and VH1 music videos had replaced movie musicals. As a former VH1 veejay, and as a lover of movie musicals, I say that music videos took inspiration from movie musicals but they did not replace them. Marketing is a main force that drives the music video. With the quick shots and edits that seem to come every :03 to :06 seconds, with the several changes of wardrobe and location or background, the main purpose is to sell the artist, present an image and sell records. When chameleon Madonna wanted to show a new image, she did it in a music video. In a movie musical, one can extend and/or present a new maturity in a star's image. The musical numbers, however, are "reveals." They are present to reveal more about the character and the character's emotions which will be important as the story progresses. In the number, a creative and skilled director -- like Vincente Minnelli -- can highlight the star's look and the star's strength as an artist.
Musicals are festive and fun on the big screen. In production, they are hard work. Notice Judy Garland's strength as an actress and a singer. There are no MTV-like quick cuts and edits from Minnelli. Judy sings in one continuous take for about 2 minutes before there's a cut for a different angle. Basically, she nailed a couple of hours of studio work in one continuous take. Her emotions as Esther Smith are fluid, spontaneous and, acting-wise, spot on for a girl who's thrilled she may be near the boy who makes her heartstrings go "Zing!" This is excellent singing and acting.
Here's "The Trolley Song" in Minnelli's MEET ME IN ST. LOUIS, thanks to Warner Archive:
Movie musicals are an art form. Judy Garland and Vincente Minnelli were masters in the art.