You make a good point...
Nobody's going to spend loads of money on space flight to "expand the species," unless it's some eccentric billionaire. People will go out there for the same reason people have gone anywhere new throughout history: elbow room, search for new resources, to escape from something bad, and in later years of history, to find political freedom and to make scads of money.
The distant ancestors of the American Indians did not cross the Bering Bridge to colonize the New World for humanity. They were either following their food supply, or maybe just running from something behind them. But the job got done nevertheless.