Why do 1800s black-and-white portraits look godlier and more solemn than modern color portraits?

I’ll instantiate with portraits of these US Supreme Court justices:

Stephen Johnson Field (November 4, 1816 – April 9, 1899)

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Rufus W. Peckham (November 8, 1838 – October 24, 1909)

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John Hessin Clarke (September 18, 1857 – March 22, 1945)

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I read https://redd.it/3fq9ux and https://redd.it/3suvbz, but I don’t understand some of the detail as I know nothing on photography.