I believe this is because the sub-Saharan African humans would be anatomically modern, while the others would not. Even though there was gene flow back into European and Asian humans from Neanderthals and/or Denisovans, it apparently doesn't count for much in their physiology compared to their sub-Saharan genetics.
But I don't think "human" excludes those groups, when not qualified. My understanding is that there's a continuum between the first archaic humans that diverged from chimpanzees and the behaviorally modern human. The anatomically modern human predates the behaviorally modern human. It coexisted and interbred with archaic humans, but is believed to be the predominant ancestor of all extant humans. (Although some argue that anatomically modern humans are indistinguishable from behaviorally modern humans.)
It's pretty wild to me to imagine that for all of our diversity and abundance today, there was much greater diversity of homonins at a time when we were much fewer in number.
> It's pretty wild to me to imagine that for all of our diversity and abundance today, there was much greater diversity of homonins at a time when we were much fewer in number.
Fewer in numbers means more isolation between groups.
In addition to that, early stages of culture may or may not have further augmented isolation. This is purely speculative of course, but we are in "imagine" territory anyways. Then the first group to develop cultural traits that somehow facilitated crossbreeding might have triggered a cascading melting pot effect, leading to the relatively uniform "modern human".
But I don't think "human" excludes those groups, when not qualified. My understanding is that there's a continuum between the first archaic humans that diverged from chimpanzees and the behaviorally modern human. The anatomically modern human predates the behaviorally modern human. It coexisted and interbred with archaic humans, but is believed to be the predominant ancestor of all extant humans. (Although some argue that anatomically modern humans are indistinguishable from behaviorally modern humans.)
It's pretty wild to me to imagine that for all of our diversity and abundance today, there was much greater diversity of homonins at a time when we were much fewer in number.