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?
Most if not all music is on YouTube for free already. Maybe the equivalent is the sites that let you download music from YouTube and these come and go like the movie streaming sites.