Or is it lack of self-awareness or honesty? Do economists imagine they understand the economy better than aeronautical engineers imagine they understand flow? And if so, why?

I'd say lack of honesty because claims are hard to verify and therefore it's all about signaling competence to gain status. On the other hand the basics of austrian economics are almost trivial and since you don't get points for stating the obvious austrian economics is marginalized although overall it leads to better results.