For example, was Bach thinking commercially when he became one of the main architects of the Baroque movement? Or, Scott Joplin thinking commercially when he "invented" ragtime?"

I would suppose that would depend on what Bach's, or Joplin's, full time job was at the time. Now for J.S.Bach we have the following:

Johann Sebastian Bach (31 March 1685 – 28 July 1750) was a German composer and musician of the Baroque period, which spanned from 1600 to 1750. - So he was a full time musician.

For Scott Joplin - Scott Joplin (November 24, 1868 – April 1, 1917) was an African-American composer and pianist. Joplin achieved fame for his ragtime compositions and was dubbed the King of Ragtime. Sometime in the late 1880s he left his job as a railroad laborer and travelled the American South as an itinerant musician. He went to Chicago for the World's Fair of 1893, which played a major part in making ragtime a national craze by 1897. - so another full time musician.

I believe that both in their own way hoped that their "style" in both composition and in performance would guarantee that they, in their own way, stood out from the pack in order to secure their living. Is that commercial?