A commenter points to a post from Pete Boettke a couple months ago, where he quotes testimony from David Colander.
One would think that competition in ideas would lead to the stronger ideas winning out. Unfortunately, because the macroeconomy is so complex, macro theory is, of necessity, highly speculative, and it is almost impossible to tell a priori what the strongest ideas are. The macro economics profession is just too small and too oligopolistic to have workable competition among supporters of a wide variety of ideas and alternative models. Most top researchers are located at a small number of interrelated and inbred schools. This highly oligopolistic nature of the scientific economics profession tends to reinforce one approach rather than foster an environment in which a variety of approaches can flourish.
I have commented before on the issue of "interrelated and inbred." Basically, a handful of macroeconomists from the 1970's had enough Ph.D "children" that their grandchildren now totally dominate macro at the top schools.
Olivier Blanchard will tell you that he and his cohort "passed the market test." To me, it looks more like a mutual back-scratching society than a market test. As Colander points out, the National Science Foundation is a major factor in this. However, his proposals to tweak the NSF process strike me as meager. To me, the larger issues are:
1. The in-breeding in the academic hiring and tenure process.
2. The fact that arrogance is regarded as a positive trait in the academic world.
The almost-inevitable result is to foster the creation of closed-minded cliques. The problem is particularly acute in macro, because the inability to construct controlled experiments means that, in Bayesian terms, one's priors tend to swamp the data.