It's a consequence of excessive land costs. If the lot costs half a million, it seems appropriate to put a big fancy house on it. This leads to too much house for the lot.
Most people's idea of a house is rather conservative. It includes slanted roofs and modest sized windows with small panes. If you build a modernist steel and glass house with stone elements in a suburban setting, you may get a writeup in Architectural Record, but it will be hard to sell.