why are no new, non-personal songs added?

As in the song of the family....? I think that as soon as Kino came under the spell of the Pearl, he no longer felt the same connection with his environment and heritage. The greed for money disturbed the fragile equilibrium needed to hear those songs.

This is from page 2, and we aren't told why there are no new songs...... only that Kino's people had once been great-makers of songs and that the songs were all remembered, but no new songs were added. We can infer that this happened because of the change in Kino's people's culture, in addition to the area's colonization.