Malbim: After Churban Beis ha'Mikdash and Bitul of Malchus Beis David via the blinding of Tzidkiyah and Yechanyah was in Galus, this Nevu'ah is about the shepherds (leaders) who caused this. They did not graze Hashem's flock in grassy areas. Hashem's verdict to nullify their kingship was justified.