According to Mary Elizabeth Funke, during a period of Meister Eckhart's life (page 18-19)
Several convents of nuns and Beguinages were placed under his spiritual direction; to them as well as to the people, who flocked to the churches, he preached in the vernacular.
Spiritual direction need not be a form academic lecturing, but rather viewed as sermons: (page 35)
Meister Eckehart is best known by his sermons. He was one of the first to preach in the churches of the Dominican nuns, to which the laity had access and whither they flocked in great numbers, drawn as much by the personality of the preacher as by the content of his sermons.
So Meister Eckhart did preach sermons to Dominican nuns and lay religious women in beguinages. The reason why this happened was because he was assigned to provide them with spiritual direction.
Funke, M. E. (1916). Meister Eckehart. National Capital Press, Incorporated.