Yeah, movies are something you have to devote your full attention to. That's why I could never devote a day to watching numerous movies/TV, which some people like to do.
Although to be fair, why would you want to watch a show with music on? You wouldn't have a clue what's going on.
On the other hand, has anyone tried watching tennis while listening to music?
I have, and it's too hard to pay attention to the tennis.
Yes I did it too, but I mute the sound of the tennis.
As for the reason to watch a movie with music on, honestly I can't give you a rational answer, it's just sometimes I think watching a movie is a waste of time. I could do plenty of other thing at the same time instead of just being focused on a single thing, if you see what I mean !