They weren't. The central problem with 2312 is that 2312 is almost unimaginative, pairing a radically transformed solar system with an unchanging Earth, incidentally giving us protagonists who are unsympathetic for reasons not the fault of the reader. Robinson has done this all before, and it shows.
The future of 2312 combines remarkable prosperity and abundance with terrible privation. An Earth ravaged by ecological catastrophes--greenhouse effect, sea level rise, climate control efforts resulting in catastrophic mini Ice Age, et cetera--is caught up trying to survive the consequences of our time's errors, with three of its eleven billions risking starvation of anything goes wrong. There is wealth and power in abundance--China, in particular, still authoritarian--but it is distributed unequally. This unequal distribution of wealth and power is not enough to keep this Earth from becoming the homeworld of a new spacefaring civilization. Mars is terraformed with speed, through technological and political processes not wildly different than those described in the Mars trilogy of two decades ago, while China leads the aggressive transformation of Venus--solettas cool the planet and let the carbon dioxide fall to the surface as ice, while icy chunks bring water and something is done about the day. Away from the inner worlds of the solar system, among the asteroids and on the moons of the outer planets and even on Mercury, a quantum computer-managed economy of abundance unites an ecologically and culturally diverse archipelago of thousands of habitats, one preparing to transform even distant frozen moons like Ganymede and Titan into habitable enclaves. On Earth, humanity remains the same; away from Earth, humanity is beginning to speciate, fragmenting into multiple subpopulations defined by particular responses to issues of environmental requirements, and gender, and sexual orientation, and longevity. Into this complex solar system, on the brink of transitioning into something new, an intrepid ad hoc coalition of investigators happens upon a troubling conspiracy.
My immediate problem with the setting is that it combines a not-quite-believable excess of success away from Earth with downright stasis on the human homeworld. Technical issues aside--would putting Venus in a permanent shade actually lead to its atmosphere freezing out into dry ice in a century or two?--Robinson's projects away from Earth involve the unmitigated success of huge megaengineering projects, involving the export of nitrogen amounting to half of the Titanian atmosphere to the Mars for the benefit of terraformers there, the fragmentation of a Saturnian ice moon to provide water for Venus, and more energetic projects still on outer worlds. None of them seem to have failed. Robinson mentions in passing, yes, that Mars terraforming had some problems, but these are not described in-depth to a reader told that Mars is now a perfectly pleasant Earth-like world. Similarly, while the particular route taken by the Venus terraformers leaves the world vulnerable to disaster--this vulnerability is key to the conclusion--this vulnerability exists firstly as a consequence of imaginable and defensible terrorist acts and secondly because of computing issues that feel somewhat contrived notwithstanding plot developments. Everything done offworld is a success, along the lines that Robinson himself described in the Mars trilogy of nearly two decades ago, and along the lines described by other authors imagining an imaginable future where everything has been done superbly with few flaws visible to the admirer. No unpleasant surprises here.
And yet, on Earth, nothing has been accomplished apart from a mini-Ice Age that led to mass death worldwide. There are many small-scale efforts aimed at mitigating environmental change in certain parts of the world, but the only big global project tried by humans on Earth was a failure. Manhattan and Shanghai may be flooded, a wide belt of territory from the Mediterranean basin west through to South Asia is desertified, and everyone is worried about a single big catastrophe that might tip the planet into a new human-hostile era, but no one does anything. This inertia is unsurprising because, it seems, Earth hasn't changed in any positive way at all in three centuries. Have the rich countries remained rich and the poor poor, with few exceptions? Has Africa remained "irrefragable" (a real word, apparently)? Does China remain an authoritarian state? Yes, yes, and yes. It felt as if Robinson was going out of the way to stack the deck, to contrast a relatively successful and dynamic off-Earth civilization with a consistently unsuccessful and unchanging Earth. The argument of many of 2312's characters that the Earth's situation was too complex for anyone on the planet to engage with felt very unconvincing. No surprises at all here, alas.
(How did the relatively progressive off-Earth civilization ever manage to form at all, given its unpromising beginnings? I don't think I quite got an answer. There was a certain amount of self-selection in the migration to space, but this self-selection seems to have created populations relatively alienated from Earth and alien in varying degrees to each other. The Mondragon economy of the progressive space habitats never quite struck me as plausible for this reason. In a single habitat, sure, but so many diverse and often antagonistic habitats? But I digress.)
Into this complexly unsatisfactory universe came Robinson's characters. They weren't badly-conceived characters so much as badly placed characters. Robinson's chosen protagonist Swan Er Hong, a temperamental ecologist and artist plunged into the investigation of the conspiracy through family ties, was an unconvincing focus of action in the story. Events did not plausibly happen because of her so much as around her. (She was involved in a Venus-related incident that strikes me as not quite believable, while her involvement in the attempted rewilding of Earth with wild animals does not lend that ill-thought plan any credibility. What happened to Nunavut's needed wheat exports when caribou and wolves colonized those fields?) Her colleague, Titanian diplomat Fitz Wahram would have been a better focus. Even better than this would have been the exiled Mars-born "small" (read "dwarf") and investigator Jean Genette, who had a very interesting backstory. Alas, 2312 had very little of the story told from Genette's perspective. Kiran, a South Asian emigre to Venus via New York City who was Swan's ally on that world, had more of the story told from his voice, and Kiran unfortunately wasn't the most thoroughly-sketched of Robinson's characters. Things happened, to different people connected in a variety of different and often distant ways, and then the novel ended.
2312 could have been a much better book. Robinson could have done a better job picking characters; Robinson could have done a better job imagining an Earth that would change as radically as his solar system did; Robinson could have imagined the megaengineering projects of offworld being complicated, and shown us the resultant meanderings. Unfortunately, for whatever reason, Robinson chose not to. Instead, Robinson built the same old future that Robinson and others have imagined before, and more freshly at the time. I'm still glad that I read the book, since there are some interesting ideas, and characters, and passages of prose like Swan's description of her arrival in a futuristic flooded Manhattan are a pleasure to read. I just wish that there had been more than these gleanings and retreads of past glories.