Why do Q&A board moderators close economics questions?
As one of the site's three moderators, I can say that the simple answer to your question is that the moderation team closes questions that are not on topic according to the stack exchange community's agreed guidelines. The economics portion of these guidelines can be viewed in the site help center, while the more general guidelines primarily involve asking a question that has a definite answer (is not opinion based), is not a duplicate, and is sufficiently clear as to be undersandable to the site's users.
It is important to note that moderators close very few questions. For example, in the last three months only 13 questions have been closed by the site's moderation team (about 2% of all questions on the site).
Questions are almost always closed (if at all) by voting among the community's ordinary members rather than by moderator intervention. Closed questions are initially put 'on hold', meaning that there is the opportunity to edit questions in a manner that makes them consistent with the community's guidelines, at which point they will be reopened. If you believe that a question has been wrongfully closed then you can flag it for the attention of a moderator. I can speak for the whole moderation team in saying that we have an open mind to including a very broad range of questions—both technical and non-technical, and from experts and laymen. We only require that questions are on topic and conform to some minimum standard of quality.
There is absolutely way too much censoring of questions by the moderators. There is nothing hurt by leaving a "bad question" up and the community already has the means to tell/vote the initial poster why their question was poorly formulated. When a moderator censors a question, they are making the forum more about them and not the community.
Many "bad questions" actually aren't bad at all, but rather are different and unorthodox. These offer economists ways to think outside of their box and mathematical formulas and instead offer thoughtful conceptual explanations to the public. Even "bad questions" are learning experiences for others who find these topics.
The other main excuse to shut down threads has been that it is a "duplicate". God forbid that you don't read every question ever posted on the forum and google every variation you can think of. In many cases the proclaimed duplicate isn't that or has nuanced differences that are very important but are not readily visible to the trigger happy moderator. Again the community already can suggest to the OP that their question has been answered elsewhere and there is no need to go to the extreme to shut down a thread that somebody invested a lot of interest in.
TRUE moderation should be for advertisements, porn and other graffiti. Not poorly stated questions.
Moderators score points answering questions that use the axioms and rules of economics textbooks. Since they know these axioms and rules well, it is beneficial to their Q&A score to not allow such impractical questions. By deterring such questions with down votes, the community of moderators is protected in their status and the benefits they gain of this status.