Space factories for spaceship. It's much cheaper to build something heavy in space and have them launch from there. Of course you would have to mine asteroids instead of sending construction materials from the Earth.
Security concerns. If you want to test some form of nanotechnology, you better do that in space and nuclearize the whole thing (provided that nanotech is still extremely dangerous).
MIS (millionaires in space): once you live in outer space as a status signal, it's easier to befriend other rich weirdos in space.
Space factories for spaceship.
You still need a strong economic reason for the spaceships if we're looking at a scarcity society with plausible tech. (Unless there's enough public and political will for exploration for its own sake which would rquire its own explanation)
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