Orpheus10, I didn't really explored modern Sub-Saharan African music, but you may be right that most of it moved to the New World.
Slavery, loss of habitat and strange new lands are obvious. But there is at least one more factor that surely contributed - daily interactions with white people. Not all slave owners were bad or mostly bad, but interaction even with bad can give a lot. Black music in Americas developed in a situation of unusual environment. Let's give credit to everyone who often unknowingly contributed.
Slavery, loss of habitat and strange new lands are obvious. But there is at least one more factor that surely contributed - daily interactions with white people. Not all slave owners were bad or mostly bad, but interaction even with bad can give a lot. Black music in Americas developed in a situation of unusual environment. Let's give credit to everyone who often unknowingly contributed.