I highly recommend the book (it is a quick and funny read) but to give you my short version: post WW2, academic architecture was taken over by anti-traditionalists, and purity spiraling lead to what Wolfe called "The Yale Box". People like Christopher Alexander[1] were ignored or shouted down as fascist, the craftsmen who were able to build the old way all died apprenticeless, and here we are.

[1] - https://www.amazon.com/Timeless-Way-Building-Christopher-Ale...