Why was the motet more attractive to sixteenth-century composers than the Mass?

In the sixteenth century, the motet became more attractive to composers than the Mass due to its greater flexibility in form and subject matter, allowing for more personal expression and experimentation. Composers could explore a variety of texts, both sacred and secular, and employ intricate polyphony without the constraints of the liturgical structure of the Mass. Additionally, the rise of the Protestant Reformation encouraged the creation of new musical forms that reflected individual beliefs, making the motet a popular choice for both composers and performers.