When and why did the decline of Musicals in American Cinema happen?

Question

It seems to me that musicals are much less common in the American Film Industry these days in comparison to the 30's, 40's, and 50's. Of course, I'm not saying that they never make musicals (e.g. Disney/Pixar films, Baz Luhrmann films, etc...), but it seems like they used to make a lot more a long time ago. When did this shift away from musicals occur? What are the factors which led to the apparent decline? Why don't we see very many american musical films?

Answer 1

I could answer, but this video does such an excellent job, I will let it speak for itself.

https://www.youtube.com/watch?v=b8o7LzGqc3E