One example: Some people who run metal bars have contacts to people in the industry, usually because they frequent these bars. And since the atmosphere is always a very friendly one, these contacts may sometimes bring a USB stick to the bar so the barkeeper can play the new album in advance to offer his guests something special (like I got to hear the last Amon Amarth album a few days early for my birthday). And sometimes if both sides have had a drink too much, the barkeeper will put the files on your MP3 player if you ask him. And then you are the one who puts it on the internet.
It's one possible scenario, there are others.
It's one possible scenario, there are others.