I think a good theory is:

Up until the late 1800s, beauty was expensive. Therefore, it was a costly (i.e., believable) signal of wealth, status, and taste. In the late 1800s and early 1900s, modern manufacturing got going and made beauty cheap. The ornate wrought iron door that took some workman hundreds of hours to produce was a good signal. Now, a cast simulacrum can be made at scale and ordinary people can have beautiful doors.

This led the tastemaker art and architecture elite to start playing a kind of inside baseball where what's "beautiful" isn't beautiful in some objective sense, or to ordinary people, it's just what's trendy within their clique at a given time.

(and, to head you off at the pass: you may like brutalism or Obama's library, but the data clearly show that regular people do not)

See Tom Wolfe's excellent From Bauhaus to Our House: https://en.wikipedia.org/wiki/From_Bauhaus_to_Our_House

Also this ACX discussion (it's a few posts) is really good: https://www.astralcodexten.com/p/book-review-from-bauhaus-to... https://www.astralcodexten.com/p/contra-everyone-on-taste https://www.astralcodexten.com/p/three-model-organisms-for-t...

We should really do something about this. Buildings affect everyone around them, and we should force people designing them to make buildings that regular people find beautiful.

These people are trying: https://www.humanise.org/

CNC Stone Carving