explain why no new songs were being added to the songs of kino's people

Kino's people were being oppressed, they were losing their culture. Thus, a people that had "once been great makers of songs so that everything they saw or thought or did or heard became a song," had lost the ability to hope and dream. They were stymied and the songs ended. But we do know that Kino possessed dreams and had personal songs of his own;

"In Kino's head there was a song now, clear and soft, and if he had been able to speak of it, he would have called it the Song of the Family."