I was at a concert of sacred music in a church. The first piece was chant, sung from the choir loft. At the end of the piece, there was no applause. Then, the next performer came out on "stage," in front of the audience, and everyone clapped as she came out. And they clapped when she was done.
This got me thinking about and wondering "why" people didn't clap for the chant singers in the choir loft.
It could be, possibly, that chant is just a style of music that does not encourage clapping. While that is true, try to imagine the same group of singers, walking out onto stage, and singing the chant, and walking off again. Of course people would clap when they walked onstage, and when they were finished.
People don't clap for things in the choir loft, or really, for things they can't see.
Leading me to conclude... (as I already knew before typing this...) that musicians during Mass should be *unseen* and in a choir loft if available, and not up front where it *looks* like they are performing, and people may even want to clap!