Church choirs exist to lead and sustain everyone's singing - not to do it all themselves

A quote from the General Instruction to the Roman Missal (GIRM):

Among the faithful, the schola cantorum or choir exercises its own liturgical function, ensuring that the parts proper to it, in keeping with the different types of chants, are properly carried out and fostering the active participation of the faithful through the singing. It is fitting that there be a cantor or a choir director to lead and sustain the people's singing.