While the legal streaming services are great, they're too expensive if you want the full functionality, and that will always limit them. When you're listening to Spotify free, you can only skip a certain number of tracks - making it difficult to try new music just in case you like it. If you can just download an album from a pirate website, you can try it and skip tracks when you like.
Music that has been pirated allows free access to listen and is creating fans who may not have heard the music if it was only available through legal streaming services. Many of the people listening to pirated music do not have the financial means to join one of the legal streaming services. If legal streaming services was the only option they would not have the opportunity to discover a lot of great music and discover new artists.
Pirating music is just like going into a store and stealing a cd. Just as shoplifting can raise prises for all of us, so can pirating. An artist deserves to get paid for their work just as anyone else does. Legal streaming sites are different because they have an agreement with the artist.
If the value of a song is based on how much someone will pay for it, logically, you could assume a song is better because someone is willing to pay for it. The average music buyer won't seek out new music unless it's presented to them like streaming services do. Streaming services do what radio used to do, promoting artists to listeners who've never heard them and may like them.