Why first-time novelists write about what they know and what happens when they don't

I am perfectly willing to cut Jon McGregor a lot of slack, as it's clear from his first novel, If Nobody Speaks of Remarkable Things (2002), that he has lots of talent, particularly remarkable for a first novel by a 20-something. I believe he has published a few novels since his debut, all of them in a somewhat experimental narrative vein (I will go back and re-read a James Wood review from last year of McGregor's most recent novel). Few writers in their 20s would have such insight into a wide range of characters of a wide range of ages and temperaments - but all living in the same block of houses in an unnamed English city (possibly London). (Who would be his counterparts in this? Carson McCullers for sure, probably Pynchon, maybe DF Wallace?) The problem is, he doesn't seem to have or to want to share any deep knowledge about the many characters in this novel; the novel comprises scenes and sketches, sometimes in first person sometimes 3rd - but in writing about so many people he skips away from writing deeply about any. Most debut literary novels are first person, almost memoir-like and that makes sense, that's where writers tend to start, w/ what they know best. By taking on a much more ambitious challenge, McGregor seems to run out of gas - and to focus more on his elaborate design and less on narrative, plot, character, setting - so by the end we're (or at least I am) confused and disoriented. There is no way that on one reading one could keep all the characters straight; there are many strange allusions in the novel - various incidents of injured or burned hands, a case of a twin who may not really be a twin but may be out of shyness pretending to be his own brother; most of all, there's a big, dramatic conclusion telegraphed in the first pages and then withheld, for no reason other than author's prerogative, till final pages. Can anyone believe in or care about the conclusion? It seems to me that McGregor had to wrap it up in some way and came up w/ an improbable sequences of events not sufficiently built up by the characters and incidents in the preceeding 250 pp. Spoilers here: What happens at the end (I think!) is that one of the residents of the street does a bungee leap (where? why? how?), people are distracted and look up, and a speeding auto hits a child at play in the street. Well, here's where McGregor's timing is unfortunate; most readers today expect from the outset that the conclusion will be an act of terrorism - as a # of novels have been built around the where-were-you-on-9/11 theme, for example - though he must have completed his novel some months before the 9/11 attacks - so the "payoff" scene feels like a letdown when read today. So, yeah, it's a first novel, and I suspect his work has become more confident and skilled as he's matured as a writer - and that he has maintained his commitment to narrative and structural experiment.