]
] In short, it strikes me that "something simple done with great elegance" was the approved style for almost anything.

We've forgotten to mention two major influences on all matters, namely the Romantic movement and the Industrial Revolution. While romanticism could get wildly extravagant, there was a notion of the Natural as opposed to the Artificial, which might have contributed to the decline of frills and adornments.

The Ind Rev brought had several fashion consequences, perhaps most notably the reduction of the cost of clothing, particularly cotton and wool. However, I can't think of why this should have contributed to plainness without getting very speculative.