... so is "smooth, impermeable surfaces" the current begrudgingly-accepted model or something? because there's no way any person who has ever been in a house would think that's a reasonable model. permeable surfaces are all over the place, literally most of the place because it includes essentially all walls and therefore wall interiors. managing that for e.g. humidity is a significant part of building design because it's completely inescapable... and that's before even touching stuff like fabric where your average couch probably has more surface area than all structural surfaces combined.
Simplifying the surface makes it possible to model the system with equations that can be solved analytically--which gives theorists something to work on. Modeling more complex systems (which often happens, eventually) typically requires lots of computing power and results in a model that doesn't generalize well.
Then again, I can't fathom what people would be doing with their money if the stock market weren't there. I imagine they might naturally wind up with some sort of...stock market.