Surprise! You're right! Joan Serrà, Álvaro Corral, Marián Boguñá, Martín Haro & Josep Ll. Arcos have written a paper, Measuring the Evolution of Contemporary Western Popular Music, where they have used the Million Song Dataset to analyze pop music produced between 1955 and 2010. These are some of their conclusions:
[W]e find three important trends in the evolution of musical discourse: the restriction of pitch sequences (with metrics showing less variety in pitch progressions), the homogenization of the timbral palette (with frequent timbres becoming more frequent), and growing average loudness levels (threatening a dynamic richness that has been conserved until today).
Or, to put it more simple:
This suggests that our perception of the new would be essentially rooted on identifying simpler pitch sequences, fashionable timbral mixtures, and louder volumes.
Or to put it even simpler:
Hey! There's less TUNE today! And everything sounds just the same and everything is deafeningly loud!!!
There are definitely worse (louder!!) examples, but this will have to do: