The author sort of brushes aside the idea that it became unfashionable due to it no longer being a status symbol in the footnotes, but I think that is basically the answer, but with another step in between.

When ornamentation became cheap and mass producible, it also frequently became _ugly_. Tacky knockoffs of appealing designs became far more common than the original decorations. So much more so common in fact that it became the default association people have with decorative ornamentation. A plain white plate is making no pretensions and is exactly what it appears to be, but the same plate stamped with a pattern is something that's trying and failing to appear fancier than it is. Worse, a hand-painted plate will be assumed to be a cheap stamped plate.