[r00fus]

Good question, one that probably has less to do with what Google wants, and what the music industry requires. If you turn off the screen, the "video" is indistinguishable from an audio stream. So they want to track for terms of royalties paid per "listen".

This is only feasible on a subscription basis (no one has a good microtransaction model with actual payments) and so Google and the music industry limited the feature to only subscription based.

[Cyph0n]

But since Google owns the Android platform, they could make YouTube track usage even when it's off-screen (paused Android activity), right? Heck, that may even be feasible without special privileges. Not sure about iOS though.

I mean, if I can minimize a tab running YouTube on my PC, I don't see why I can't do that on my phone.