A calling card is only a brief representation. If Memory was all there was to the show, the stage audiences would walk out as soon as it’s sung.The other interesting thing about the trailer -- apart from the fact that it looks ridiculous -- is that they went and used Memory already.
On the one hand, it makes sense to use the most well-known and iconic song in the trailer.
On the other hand, it's the most well-known and iconic song. There's no topping it. So they've already revealed by far their best number in the trailer. So, what's left to be the calling card for the film?