I don’t think your last sentence follows. Like I noted if they have the technology for interstellar travel I sincerely doubt they wouldn’t also be able to transfer larger populations across those distances. Even that idea might not make sense in this context. Perhaps they’d store their genetic code and simply grown the colonists upon arrival. For us yes we shouldn’t think of colonizing the solar system like it’s just a new continent, but that’s viewing it in the context of our current technology levels. If we had interstellar travel available suddenly that equation changes considerably.

Human life already relies hugely on an artificially created habitat to satisfy basic needs. The trend is to become less coupled to the natural environment that we evolved within. Perhaps that could one day include self supporting habitats beyond the surface of earth. But I do wonder if the focus on planetary surfaces is desirable. If we can survive on the surface of Mars then perhaps space stations/ships could also be self sustaining? If there is enough material outside of big gravity wells then why not?