Q: Why do we have easel paintings?
A: The emergence of middle-class art collectors.
“In [17th century] France, as the new rich and the noblesse de robe multiplied and the old noble lines died out or needed to recoup financially, the dealers became essential to domestic art transactions….Particularly important was the easel painting which had become, through the influence of Dutch fashion, a middle-class substitute for the too-expensive floor-to-ceiling canvas in a luxury mansion.”
From Harrison C. White and Cynthia A. White, Canvases and Careers: Institutional Change in the French Painting World, 1965.