Good question. Perhaps the abortion debate backstory is considered too heavy or controversial for a mainstream audience. Similar problem for Gerald's Game. I'm sure even the Hollywood folks don't understand, though, why some movies get made and others do not. It often seems like a matter of chance.
Good point - I suppose we've all been brainwashed into being ultra-PC these days that we're supposed to be offended by everything
What better way to debate the Pro Life/Pro Choice situation than in a story that views both sides equally? - certainly better than sweeping it under the carpet - still Hollywood would rather churn our countless sequels than do anything original
I suspect this one is a simple equation. There is very little "action" from a Hollywood standpoint in this book. The conflict both internal and external is very intellectual for the most part. Hollywood will always gravitate towards script treatments of novels in which there is more of the things they are better at showcasing. With that in mind, think about how long and hard they have been trying (and still haven't managed to achieve) to get the Gunslinger made into a movie. I expect Insomnia will be pretty far down on the list.
Back in 2007, there was talk of a deal that was made to produce Insomnia with Rob Schmidt (Wrong Turn, The Alphabet Killer) directing. But beyond that announcement, I can't find anything about it, and it certainly was never produced.