I think Van Gogh was taken by the motion inherent in Delacroix’s presentation. He loved it so much, he did one of his own. It appears that Van Gogh worked in the priest and the Levite as well (though those might be the robbers).
One man hoisting an inert full-grown male onto a donkey requires tremendous motion and exertion, which Delacroix captured and Van Gogh emulated.
Van Gogh knew a thing or two about people turning their backs on him, so no surprise he included them in his version (which would seem essential to the parable).
Amazing find, that painting!