Nothing is worse than a meeting when nobody is really in charge. The proceedings go off topic, conversations last too long, people lose interest, bullies arise who try to save the day, and little beautiful happens.
It is the same with music. Aug! Have you ever gone to a Mass where there is no organist or leader and someone starts a song - maybe it is even introduced by the priest, and it gets slower and slower, maybe changes key, someone in the back starts trying to rally the troops, some roll their eyes and wag their heads and close hymnals . . . why even bother trying?
I find it painful.
Paragraph 104 calls for a choir director for the Mass. If there is no choir director, then the cantor needs to be able to lead the singing. This person is chairman of the (musical) board. Like a good leader of a meeting, they make sure we are on the agenda (so to speak), are proceeding in a way that keeps interest and encourages participation when called for, and does so with craft and decorum.
It’s not just about singing. It is about making something beautiful. Beauty inspires, lifts, directs. Music for the sake of having music can be torture. If you are going to do it, do it as well as the community can muster. Those present deserve beauty whether it is because they are listening or they are asked to participate in which case they are part of creating that which is beautiful when giving glory to God.