People forget about Google Music because Google seems to have forgotten about Google Music. Same with Google Voice. They don't push it, no one will use it. Personally for me, I switched from Google Music to Spotify because Google boycotts Windows Phone. I don't have the patience to put something in my workflow that doesn't work on every platform I use.
There are a lot of good streaming music services, but Spotify is the only one that seems to be committed to working everywhere on every device. That means a lot more to most people than having a specific artist or audio quality.
