I suspect that, in many walks of life - the arts, business and finance - financial success requires a one standard deviation intelligence. Writers must be sufficiently smarter than their readers that readers feel their intelligence to be flattered, but not so much smarter that they appear weird.
This sounds like an echo of the observation I come back to far too often for my own comfort: It's the idea of the original that people respect more than the original thing itself.
I suspect this becomes proven most bluntly when it comes time to put the original thing in front of a paying audience. The more one tries to be "original", the harder it becomes to find people who are willing to meet you half-way.
A big part of that, I think, is that most people are not critics or artists — they don't want to be, and we don't provide them with much of a social impetus to be that way. (Our idea of the artist is someone Up There (or Out There), with the rest of us Down Here, enjoying whatever blessings get showered down on us by their good graces — a view that's misleading to both sides.)
End result, there's a strong pressure on people who care about their art as a trade or a business to stick to what's known because it's most easily marketed to others. There's less of an incentive to not repeat what's been done before; the work involved in making such a thing comprehensible to others is at least as hard as the work put into the work itself.
My sarcastic way of putting this: "Don't be too original."