> I am skeptical this is the origin of modern decor. The trend away from ornamentation, toward simplicity, flatness, etc in design goes back several generations and transcends interior design.

You should be. Modernism is an ideological design response: the aesthetics of the machine age and utilitarianism.

OP's opinion is not based on actual design and architecture history and (ironically) appears to be itself an ideological narrative: a posthoc criticism of Modern (yes with cap M) design which itself has its root in conservative reaction against the (asserted, alleged and possibly true) socialist tendencies of the elite social and design circles that gave birth to Modernism. Note, for example, the 'emotional' appeal to long lived in homes, etc.

https://www.bbc.com/culture/article/20230103-the-historical-...