The spiritual leaders do not comprehend what is really going on, and neither are they leading the people in sorrow over that. As spiritual leaders they are to provide leadership to the people in serving God.
The priests have another special reason for leading the people in this display of mourning: after all, food and drink offerings will no longer be brought into the temple (see Joel 1:9), and this must first and foremost be of concern to the priests.1
13 Sacrificateurs, ceignez-vous et pleurez! Lamentez-vous, serviteurs de l'autel! Venez, passez la nuit revêtus de sacs, Serviteurs de mon Dieu! Car offrandes et libations ont disparu de la maison de votre Dieu.