So I'm thinking here about the sort of setting like Eclipse Phase, in which virtually all of humanity lives in a wide range of space habitats because of an apocalypse on Earth. I am imagining a variation of this without the apocalypse on Earth.
What could serve as a valid motivation for so many people to live in space without this apocalyptic assumption? Why might most of humanity abandon a viable Earth?
I'm assuming technology including fusion power is possible, as it would virtually be a requirement for stations like this. Eclipse Phase also uses transhumanism to justify some of its habitats but that isn't really a requirement for this, as you can just use O'Neil Cylinders instead.
My idea here is a sort of space opera setting that has a wide range of space habitats as the main setting, so that you can have a range of interesting conflicts within the solar system while also having reasonable travel times between things most of the time, with longer travel for stations orbiting different worlds.