What Marc is saying is the same rational used in the visual arts and movie industry. The industry pundits decide what is 'hot' and all the 'creators' rush to go that way and be the first to come up with the next hit, but within the 'accepted' style.
In the Art market, say NYC, the galleries decide what the next craze is based on sales. They might say to an artist, "African style is going well this year", so the artists all run to their lofts and crank out African style.
Movie producers do the same. They say, "Murder Mysteries are the thing", and a guy with a Sci-Fi idea can't raise the money to get his story on film. If he does find some money and his film sells, then the money changes direction until the next big thing comes along.
If a writer can get his idea heard, and it is a good one, He may find himself on the crest of a new wave of style. As writers, we all need to take that left turn and explore those little rabbit trails to see where they lead IF you are an 'outsider'. The insiders have to follow the trend or fall out of favor (what have you done lately?). This little opinion may be an over-simplification of a complex problem, but that's the way I see it.

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