I believe there exists an ideal length for a given book, song or movie. That does not mean that the same theme cannot be recreated in a more minimalist or expansive way but then it is a different work. Take Annie Hall as an example of a film which feels just right at an hour and a half.
Successful authors often produce more complex and expansive works as their skills grow. But the success can also inflate the egos, and then the length grows as any output seems suddenly worthy of preservation. The results are Metallica’s St. Anger full of endless yet uninspired songs, the Harry Potter series which even some fans admit does not need to be 40% longer (When I saw the Order of the Phoenix in a bookstore I thought it was a ‘cumulative’ edition. When I realized the mistake, I decided to wait until Rowling edits the heptalogy to be shorter than War and Peace.) than the Bible, and extended versions of movies. The popular culture, and especially Hollywood, is influenced by the dogma that bigger is better.