Egyptian is the language of the people who stayed put

After the pre-proto-Semitic speakers left Egypt for the northeast, the ancestral Boreafrasian language stayed behind and then split in two. One branch became proto-Chado-Amazigh, the common ancestor of the Chadic and the Amazigh languages. The other ran down to ancient Egyptian. The westward departure of the Chado-Amazigh speakers fits the early Holocene, about ten thousand years ago, when a shift to wetter conditions let people settle across much of the northern and north-central Sahara, and the archaeology of that period shows them doing exactly that. The communities that remained on the Nile kept speaking the tongue that would become early ancient Egyptian several millennia later. Egyptian was the last branch of the Afrasian tree still growing in Egypt. It is what was left after seven thousand years of departures, northeast into the Levant and west into the grasslands, by a population that kept shedding daughter communities while staying on the river that would carry its name.