system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How did sites like Grooveshark, Spotify, and Google Play get all that music available for free streaming?
gpt
Grooveshark is currently in a number of lawsuits over copyright infringement.

Spotify has licensing deals with music studios so that they are allowed to stream music on demand.  On the free version, they pay for these license fees with ads.  In the US, due to streaming music laws, anyone can use music for Internet Radio, assuming that they pay a set royalty fee.  This is how Pandora and Spotify Radio work.

Google Play All Access is similar to Spotify in that you need to pay $10/month and they use that money to pay for license fees to the recording companies.

iTunes Radio is different in that it has worked out license fees with companies for streaming so they can operate in many more countries than something like Pandora.  Pandora only works in the US, Australia, and New Zealand.  While iTunes Radio is initially only available in the US, many people believe that because Apple's licensing deals span across many countries, it will be able to spread far easier than Pandora.