The music was set free by the mp3 file size combined with dcc fserves on IRC, Napster just jumped on that bandwagon and leeched off the existing system.
Some of us were around before Napster showed up and pretended to be doing something new. You could've implemented Napster as a set of polished mIRC scripts, which is what it essentially was (and wasn't nearly as capable as existing options).
The one thing Napster did was make it quicker for 'anybody' to get music without having to learn anything about the underlying tech or infrastructure. The music had already been set free by the time they showed up, and the number of people in that sharing scene was growing exponentially regardless of Napster. They did such a good job of believing their own bullshit, they managed to get others to believe it, and hit a critical mass and finding music simply became most convenient by using their app. That's why they are remembered. Marketing, PR, and wasting a LOT of investment money, all for the sake of being lazy about downloading music for free.
Gnutella and to a limited extend WASTE did a better job of furthering the spread of music once Napster began to fizzle, as they weren't subject to a single point of control that could be dismantled. These days, even I use Spotify, but it sometimes feels like a step back, as does all this 'cloud' stuff. Storage is so insanely cheap that we don't actually 'need' cloud storage, but like Napster, it all plays to the laziest common denominator.