Hear me out. I love Sweeney Todd but these people didn't know it was a musical. About 15 minutes in one guy said "Are they going to sing the whole time?!". More than a few people got up and left and I honestly had never seen that before.
I guess the marketing for it at the time just completely left out that it was a musical.
If I had gone and seen it in theatres I would not have known that it was a musical based on the advertisements.
The same thing happened with me and my mate when we went to see Chicago. I guess we didn't catch any of the trailers that showed it was a musical, so we went in thinking it was going to be a gangster film akin to Goodfellas. We stayed for the whole viewing though.
Just... In general musicals never seem to advertise as musicals. I had no idea the new Mean Girls was a musical after watching the trailer, and only found out through word of mouth. The new Wonka was also a musical, I thought it would be cause the previous two were, but you never know. Trailer didn't seem to indicate. I just saw one the other day that looked like it was a musical cause it showed a lot of dance ensemble, which these trailers really should do.
EDIT: IF. Thr new Ryan Reynolds movie about imaginary friends... is it a musical? A lot of ensemble dancing in the trailer but I don't see anything indicating it's a musical. Why can't musicals just be up front with this?