There's no real reason we can't build beautiful buildings
There is a real reason: lack of skilled trades. Those old, beautiful buildings are the work of skilled tradespeople such as masons (skilled in stonework), master carpenters (skilled in joinery), glaziers, plasterers, painters, sculptors, blacksmiths, ironworkers...
Modern buildings use so much metal and glass because these materials don't require skilled trades to mould and shape them on site, they are delivered whole and assembled according to plan. To build an old-style building today would cost a fortune because the few surviving practitioners of those traditional trades are considered highly specialized experts and historians of construction techniques.
Even simple brick masonry work seems like it's dying. My father was informally trained by old school Chicago bricklayers. I'll see brickwork done by him 20 years later still looking new, and lined up well, while a lot of newer stuff just looks terrible. Same thing here in Chicago, so much nicer old brickwork compared to newer construction.
Yeah. Construction is in a race to the bottom, cost-wise. In my city (university town) there are a bunch of off-campus high rise residence buildings. They put these things up so cheaply that a lot of them are falling apart not even 5 years on!
Their whole m.o. is to put up a new building, sign as many incoming students as they can to leases, then mysteriously fall behind schedule for the opening of the building. This leaves hundreds of students stranded without a place to stay at the start of school term. They then offer these students a “free” lease transfer to the old building, thereby renting out a bunch of crappy rooms no one wanted in the first place.
Back about 20 years ago, a development where I lived got new sidewalks poured. On looking the work over, I decided that in the modern market today's foreman is the apprentice of two years ago, at most.
The other portion of this is a lot of buildings are build by contracting firms, not architects. It's taking a lot of trends and squishing them together in a way that works, but is not designed. The end product is facades with windows not lining up properly, weird perspectives, and extra rooms that don't fill a purpose.
This is a component for sure, but you can absolutely get CNC’d millwork to add ornamentation if you cared to. We can develop technologies to make buildings both beautiful and easy-to-construct if we cared to.
Also we need to be training up skilled tradespeople in general, even for the basic basic stuff.
There is a real reason: lack of skilled trades. Those old, beautiful buildings are the work of skilled tradespeople such as masons (skilled in stonework), master carpenters (skilled in joinery), glaziers, plasterers, painters, sculptors, blacksmiths, ironworkers...
Modern buildings use so much metal and glass because these materials don't require skilled trades to mould and shape them on site, they are delivered whole and assembled according to plan. To build an old-style building today would cost a fortune because the few surviving practitioners of those traditional trades are considered highly specialized experts and historians of construction techniques.