[cuboidGoat]

By the end of this century I suspect there will be more than a million people living off earth, with the majority in orbitals.

In about 200 years or so, I wouldn't be at all surprised if there were more people off earth than on it.

[chr1]

What would be the incentive for living off earth for such a large number of people?

I really wish for you to be right, but with population growth slowing down, and possibility of building floating cities or terraforming Sahara, building large orbital stations or going to mars in large numbers may be economically not viable, unless we invent something radically new.

[Kim_Bruning]

Same incentive as everywhere. They get paid. ;-)

Even the most automated of robotic factories on earth still have a number of humans in an oversight role, where they make themselves quite useful.

The same would be true of any space industry. People would be hired on for a tour in space, and they'd be paid sufficient salary to make it worth their while.

[cuboidGoat]

I think there will be two things. One is economics, fetching asteroids could be very big business, and the other is political, space will be viewed as freedom of a sort, given the kind of restrictions that may be in place on Earth by then, with the climate transforming alongside having a lot more people than we do today, even if growth slows down, which is far from certain. We could easily be in the age of what Bruce Sterling refers to as the Khaki Greens, aka, militarised enforcement of ecological protection.