Back stories in City on Fire and elsewhere and how publishers deal with them - or could

The second part, or section, of Garth Risk Hallberg's City on Fire seems, so far, to consist of the back stories of several of the characters, not exactly minor characters but those who seem to this point to be tangential to the main plot. Each of these back-story chapters is good in its own way, but I feel a little frustrated - GRH managed to really get me involved in the plot and now he seems to have pulled back and said, let's slow down here and let me tell you about each of these people, about their lives before the confluence of events that sparks the narrative. The back-story chapter feel separate and distinct - I almost wonder if he composed them separately, perhaps even before he began weaving the strands into a literary narrative. I can tell you for sure that if GRH had submitted a 400-page manuscript and earned a modest advance his editor would have said (if he had an editor, that is), cut this extraneous stuff and cut back to the chase. But a 900-page novel and a $2-million advance - it's leave everything in, everything that can make this book seem, look, and be big. Does the world have a place today for 900-page novels? Or longer? I've seen, lonely on the shelf of my town public library, a massive novel by William Vollman, and I can't even imagine reading it - I literally don't believe my hands could hold it. Someone's buying it and maybe even reading it, I guess, but I doubt anyone's making money - not till the TV series is made perhaps (same for City on Fire). To share some experience from my own writing, my publisher at Soho did ask me to cut some back story from the manuscript of Exiles - a chapter in which several war resisters recounted at a bar the experiences that drove them to exile in Sweden, and another section or two I think - and that was great advice. The novel didn't need that, and it was pretty long anyway. She also asked me to cut 4 letters that the protagonist, Spiegel, received from his girlfriend back in the States. These letters may have interrupted the narrative flow, briefly, but I regret cutting them: much of the criticism of the novel concerned the lack of motivation, why did Spiegel go to Sweden and risk so much?, and I think these letters helped set the political and romantic context. Oh well. I had always envisioned perhaps an online version of Exiles - and of any novel - in which these "cut" chapters could appear as options, like extras on a DVD for example - but publishing, in its glacial way, is not ready it seems to make these accommodations to the preferences and ideas of writers - or readers.