I’ve heard many people ask this question and I think they simply don’t understand the reality of early human migrations. The reason there is scant to no evidence of the migration of our early human ancestors is because —-
They were HUNTER-GATHERER peoples who were also nomadic and such people leave little to no evidence of their migration routes.
So it’s not surprising that when we consider migrations out of Africa (or anywhere else for that matter) that we find no to little evidence of these migrations of early hominins.
So when we think of Homo erectus migrating out of Africa in to the Levant and Asia OR when we think about this early human ancestor migrating from Asia to Southeast Asia and into Australia we MUST keep in mind not only was H. erectus a hunter-gatherer but the sea levels were considerably lower than they are today. And that means that any evidence of the migrations of H. erectus or any other hominin out of ANYWHERE is likely buried under the waters of the seas.