The idea that a lack of a mass migration invalidates the concept of colonizing space is false based on historical precedent. DNA analysis indicates all the humans outside of Africa descended from only a few hundred people. I believe their descendents now far outnumber those who stayed in Africa. The descendents of H. Ergaster and whatever the ancestor of H. Florensis was that left Africa lasted the longest other than the H Sapiens branch. The descendents of H Sapiens that left Africa founded the most technologically advanced civilizations several times in the Middle East, Americas, China, India, and Europe.

As I big supporter of human colonization of space I have never imagined a mass migration. It makes no sense. Most people don't move long distances unless pushed. The worst places on Earth appear more habitable than any place in space currently. Only a small fraction ever have the motivation to give up the safety of the known for the potential of the unknown. The risk takers/leaders are the minority simply because the odds favor playing it safe most of the time with a lottery style jackpot for the adventurous on rare occasions. If Earth is abandoned intentionally by humans it will be a gradual process as less and less of the Earth becomes habitable as the sun ages and the technology is developed to make existing and artificial worlds habitable. It is far more likely humanity will cease to exist on Earth unintentionally from man made or cosmic catastrophes. At that time humanity will cease to exist except for the descendents of those brave enough to adventure out into space for whatever individual goal motivated them.

Regards,
Mark