According to what you said, there was a notoriously parallel process in Latin American folk, with some difference (as I can see) in the influence of African and native rythms and singing. It seems that white patrons were somehow more permissive in the South, thus you may find a lot of South American folk music that is directly based on African, or is plain African, like Uruguay's CANDOMBE or Brazilian BATUCADA. These rythms and songs influenced by indian native music, established a base for the most popular, most "country" and less internationally known of our folk. Musicians of the cities, many of them educated in European centers of culture, developed the outstanding traditional music that crossed our borders.

The singing voice then evolved from Spanish music which required educated voices indeed, and this "classical" era lasted much longer than in the North, perhaps for two reasons: 1) the culture of the microphone and the society of the big city took longer to develop in the South, and 2) since the second half of the 19th century there was a strong migratory current from Italy, bringing a popular tradition of "bel canto" to these lands.
Then the most traditional songs of South America are still based in the loud and brilliant (if not educated) voice, as you may appreciate in Mexican songs, Venezuelan joropos (remember Alma Llanera?), Paraguayan guaranias, and even Argentine tango-song. (Tango is a history by itself).
Besides the fact that black population in South America, particularly in Chile, Argentina and Uruguay, was much lower than that in the North, it may be possible that the strict Catholic church in these countries never allowed black people to bring their songs to the church. (It did allow natives to sing in church, as long as they learnt Spanish-origin psalms). Meanwhile in North America, black people were giving origin (or making great contributions )to gospel, spirituals, blues and jazz and fervorously adopting their master's religion and enriching North American music for singing.
But then, are North-NorthAmerican folk songs a separate branch as it refers to the singing voice ? Is the folk singer different from the gospel and blues singer of the South ?
Thanks for an enlightening conversation - Un Abrazo
Andrés