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?
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Oh, make no mistake about it, you absolutely are. But OP asked about free options, and Spotify is one. A bad one, but still one.