pdjennings said: "It always amazes me the lengths that trailers for musicals will go to in order to hide the fact that it’s a musical. You saw ONE fragment of singing. That said, looks wonderful — cannot wait!!!"
As others have said, you'd really have to be stupid to NOT get from this trailer that it's a musical...
However, to answer your question -- sometimes trailers tend to hide the fact that the movie is a musical. That's because it's a "lose/lose" situation. On the one hand, you risk alienating people who do not like musicals. Then on the other hand you get the people who claim to love musicals -- but then prejudge the films based on a few seconds of clips and then go on to post ridiculous comments such as...
TaffyDavenport said: "Something about the snippet of "I'm Here" looks off to me. Fantasia was naturally physically expressive when she sang that song live, but here her movement looks inorganic and over-directed. I know it's only a second or two, but, out of context, it immediately read as cheesy to me.