Humans prefer humanistic architecture, with fractal visual complexity and natural materials. Modernism tossed it all out, then the post modernists recognized that that was a horrible mistake, but decided it was too uncool to just go back to what people actually liked.
If you are interested in a short US-centric read on how the whole thing went down, read this:
Post WW2 architects have a lot of human unhappiness to answer for.
But that said, the Amsterdam School and the WPA work were beautiful, and I'd never heard of them before. Thank you for mentioning them! I'll be sure to look into both in a lot more detail.