Simply put, because he loved God more.
The most radical change which Zwingli made in the Church service at Zurich was to do away with both instrumental and vocal music. This action was the more strange since Zwingli himself was a very accomplished musician, being able to play upon different instruments and also to sing well; yet in the course of the year 1525 he suspended the choir-singing and on December 9, 1527, had the organ of the Great Minster broken up and insisted that similar action should be taken by the other churches in the city and canton.
His motive was twofold; first, because all this music was inseparably connected with the Roman Church worship and he desired to remove as far as possible the Reformed congregations from all association with the past; and second, because the words of the music were in Latin and therefore unintelligible to the people and he desired to have every part of the Reformed worship in the vernacular.*
If music doesn’t serve worship it doesn’t belong in the Service. Modern churches could, and should, learn from this important theological principle. Indeed, if people were honest they would admit that most music in churches has more to do with entertainment or the self aggrandizement of the musicians than it has to do with the Glory of God.
*Samuel Macauley Jackson, Huldreich Zwingli: The Reformer of German Switzerland (1484–1531) (Heroes of the Reformation; New York; London: G. P. Putnam’s Sons; Knickerbocker Press, 1901), 290.