The author keeps referencing "cardboard modernism" but really should just use the word "postmodernism" to describe the era we are still in when it comes to construction, furniture, etc.
The reason things look and feel "cardboard" is because in a postmodern world, many objects are approximations of the objects we associate them with. So, for instance a vinyl window is made to look like a wood window which was designed in such a way because of the limits of the material in addition to the function of the object. And example being window moldings on a sash window. For a wooden window they had a functional purpose (enclose the weights and ropes) which has been lost but approximated in a postmodern vinyl window because "that's how windows look".
Materials in general have changed so much as well. So much furniture is made out of engineered wood instead of wood for example. But this shouldn't be a condemnation of our postmodern times necessarily. These types of materials, manufacturing, and assembly have made things accessible to many more people. If you want high quality objects made from fine materials and craftsmanship it is still out there. It's just extremely expensive. It's a huge gap from builder grade to quality to custom.