That's a strange phenomenon I've also noticed, since posters here usually have the opposite instinct in any other field. Most systems end up complex and difficult to model by simple rules, unless you restrict your model to a specific range of parameters or behavioral regime. Do you want to know how increasing or decreasing pressure affects fluid flow? Most knowledgeable people would immediately say that it depends: does the pressure change impact the flow regime? If it stays within a flow regime, there is one answer. But if it changes from laminar to turbulent flow or vice-versa, the answer may differ. What initially seemed like a simple relationship has a confounding factor of macro-scale regime-switching.
But in economics, HNers feel somehow confident just giving a blanket answer without analyzing the situation. Price and demand of restaurants are linearly related; raising minimum wages increases unemployment; etc. Blanket statements they'd never make in an unqualified form in fields they actually know about, somehow become fine in a field they haven't studied. Nobody seems to feel the need to inquire, well, is it a simple relationship, or can changes in a parameter change the operating regime? Very strange.