Very good points.
Are African Americans feeling the need to learn an African language because it gives them a sense of re-connection to Africa? After all, one of the successful ploys used by Europeans in the American slave trade was to deny Africans the opportunity to speak in their native tongue to make it difficult for them to plot an uprising. But even so, it was difficult for Africans to communicate among themselves on slave ships anyway because we came from so many different parts of Africa which, as you say, people spoke different languages.
I'm not sure that every African American that wants to learn how to speak an African language actually intends to use it, but it might be more of a 'romantic' notion than anything else. It could also be a form of rebellion to blatantly demonstrate that although we live in America, we don't consider English as our only language. So it could be a socio-political statement as well.
More and more, English is (or has) becoming more widespread around the world. Learning an African language is great if it empowers you. But as far as a r/evolution for Black people in America, we need to speak the language that the great majority of us understand, and ebonics works for me.