Because nobody's gonna use GDrive how Google wants them to until Google's upcoming social platform launches. _Then_ people will actually use the service to share personal files.
I dunno man... I might be willing to pay ~$2/month for an app on my phone that would stream all mainstream music at decent quality over the cellular network. Imagine a package deal for people who don't already pay for 3G data plans. Like $5 or $10 per month for unlimited listening to whatever you want wherever you are. I'm not expecting it to happen, but it sounds cool to me.