Jazz, a fusion of many musical elements derived from the African American experience, emerged as a unique American classic. Because of the African American approach to making sound, the part of the human vocal chords most utilized had its origins associated with the falsetto. Chants and choral sounds were long associated with South Africa; other parts of that continent were falsetto based.
Most of today's pedagogy does not give importance to an understanding of vocal development from a falsetto perspective, particularly when training the male voice.
The falsetto is totally self manipulative.