Because it is incompatible with the beliefs of my tribe.
Because it is clear and simple, and therefore unfit to signal my sophistication.
Or because there are some specific technical reasons why it is wrong.
I guess these are the three most frequent reasons, perhaps even in the decreasing order of frequency, why clear and simple answers are wrong.
Because the problem is complex and your clear, simple solutions has at least 3 knock-on effects, one of which will make the original problem worse. And the other 2 will cause new complex problems in 10 years time.
The clear, simple solution to "X is to expensive" is "Declare a cheaper price for X by government fiat."
By the time you have compensated for the knock-on effects, regulated to prevent cheaters, and taxed to pay for costs, the solution is no longer simple.
People want to tell everything instead of telling the best 15 words. They want to learn everything instead of the best 15 words. In this thread, instead post the best 15-words from a book you've read recently (or anything else). It has to stand on its own. It's not a summary, the whole value needs to be contained in those words.
I'll start in the comments below.
(Voted by the Schelling study group as the best exercise of the meeting.)