Several movie and TV sites have come and go where you can just visit and watch without even creating an account. Quality might not be as good as a paid service and they are no doubt in the grey-to-red zone legally. I don’t see the same service for music.
Why do you think is there such a difference in trends?
I’m fairly certain any publisher could charge advertisers more money if they could prove the ads are being watched or listened to. And the advertisers would be happy with that.