With regards to http://legalsmeagolandzeteticelench.blogspot.co.uk/2017/09/fan-theories-2.html and http://legalsmeagolandzeteticelench.blogspot.co.uk/2017/09/a-few-statistics-on-culture.html perhaps the first Orbital builders were part of a conglomerate representing several panhuman civilisations. They could have any number of reasons for doing so: to make a gigantic point about inter-civilizational co-operation, as experimental art, as well as providing extra living space. The point about Orbitals, from the perspective of an expanding and militarily suspicious civilisation, is that they are individually much easier to defend from space than a planet is. One can simply provide sensors throughout the base structure of an Orbital alongside a Hub or ship stationed at its exact centre. A planet would need to be surrounded by satellites or otherwise guarded by at least six warships. An enemy could simply play hide-and-see...