How come music leaks to the internet more then movies?

I don't understand why music lets say from Lady gaga, Britney spears Jay-z, Beyonce, Timberland, etc leaks to the internet more then movies like Harry potter and the deathly hallows part 2. Why is that? I never hear of major corp movies leaking to the internet but music just so happens to do so. Are the music artist leaking the music on purpose? I don't get it?