These days, at the beginning of nearly everything, in addition to being asked not to take photos, make recordings, or shoot videos, and in addition to being told to turn their cell phones off, people are also being asked to turn off everything with a luminous display, since it is impossible to list the range of other devices that people now bring to, and attempt to use during, theatrical performances. I suspect this, and not any sort of deference to high art, is why your "Messiah" is not photographically interupted.

For myself, I nearly never take pictures of folksingers, for the reasons that Liz has put forth. If you want good pictures, actors are the ticket, as they have studied such things as smiling, keeping their eyes open, and standing straight.