I think the reason might be mechanisation and mass-production. Before that, everything was done by hand, so it wasn't that much more expensive to produce interesting architecture or say hand-crafted ornaments details on buildings. Right now, costs of that would be gigantic (which is shown in giant costs of renovation of historic buildings, which needs to be done using the older methods), compared to a standard boxy builds which can be done using prefabricated components. Beautiful buildings would be much more expensive than standard glass boxes, so for the most part we choose not to build them.
Also, materials. Natural materials such as wood or stone feel so much nicer than concrete or glass.
"Natural materials such as wood or stone feel so much nicer than concrete or glass."
To you. But not to me, which is why I choose to live in a house with glass and metal as the primary aesthetic. But stating opinions as fact is a nice way to generate engagement, especially if they are unpopular, hence the article we're all discussing.
From the industrial revolution to some time in the early-to-mid 20th century, materials were more expensive than labor. It made total sense to ornately decorate things as the cost was not much more than the material itself.
Now labor is vastly more expensive than materials. Making this easy to build makes them way cheaper.
Still way more expensive than just laying cheap, factory-made bricks or pouring cheap concrete. Not to mention, at least in most of Europe, the buildings are expected to be thermally insulated, which is usually done with styrofoam on the outside walls (whereas, in the past we didn't have styrofoam so buildings just needed to have a lot of thermal mass (which in practice meant thick walls), which also made them more interesting and prettier). Placing the ornaments on top of it is not great solution, since the styrofoam has limited lifespan.
Also, materials. Natural materials such as wood or stone feel so much nicer than concrete or glass.