I have a little understanding of architecture, and can maybe speak to the "end" of postmodernism in architecture. Again, I'm not sure postmodernism is dead in architecture, but there is active work in "modern" architecture that is neither postmodernist nor modernist in character.
Modernist architecture was characterized by lack of ornamentation. That was not because of a dislike of ostentation, it was because nothing was included unless it could be justified by a rational principle. Modernist architecture was just the natural continuation of the neoclassical architecture that preceded it. Classical / neoclassical architecture emphasized symmetry and other kinds of mathematical order, but modern architecture took it to the extreme, and also new building materials rendered some of the elements that originally had a practical purpose unnecessary, resulting in a very minimalist style.
Postmodernist architecture, of course, eschewed the idea of having any rules.
Post-postmodernist architecture takes a middle road. Rules like "form follows function" are regarded, but not slavishly observed. The subjective effect the building has on the human psyche is considered.