It's due to marketing experts and analysts (note the first 4 letters of that) Who, likely fresh out of High school, and knowing everything, recommend useful things for an "enhanced" browsing experience. I think they are the same geniuses who place 13 green "Download" button on a software site to download a zip opener or magic registry cleaner, totally obfuscating the real software you went there for.
They want us who consume their goods and services to be a more "satisfied consumer" by pissing us off, not realizing ads, buttons, music, and silly videos will likely drive people away. Surely they have taken 3-4 days of intensive classes to learn their trade and how to predict, with unerring accuracy, what the public needs.
Their web designing prepares them for better careers at MS R&D and Software Development teams to determine what the best OS is and what we want. some may go to Google as well. I think the rest end up in Congress or mayors of large cities. One even became President recently and shows how this training plan can succeed for about anyone.
Once they earn the higher positions in the corporate and public arenas, they can stop working and instead focus on being sought after advisors to those on the way up. As an advisor one can earn thousands per hour with speaking engagements without any further training.
In conclusion of this satire it shows the unwanted music on websites does serve to help idiots, morons, and dolts to have a good life, in effect giving us all a nice warm feeling. One can also get a warm feeling by wetting one's pants.