Copyright: It facilitates piracy, both virtual and physical, hurting copyright. The MP3 format is not a format in which you can encode or encrypt rules regarding copyright, so it is very easy to buy a song, audio book, etc. It can be massively shared without any royalty to the authors. Despite this, the major record labels have known how to adapt to this problem. In a more earthly sense, small artists can suffer the plagiarism of their music if it has not been recorded before.
I fully understand your outrage and disappointment. I also hate when I am forbidden to use elementary things like music a century ago. I love classical symphonies and prefer to download mp3 from a dedicated resource. You can follow the link and find something for yourself. This site does not require registration and has the largest catalog of music in different genres.