Don't think that's the main reason. Hollywood has no compunction or lack of skill to embellish or dramatize a mundane life if they need to.
I suspect Bach's place at the top is received rather than recognized, which is not to say he doesn't deserve it. His skill lays in counterpoint and other facets of harmony. His music has structural elegance and ornamental beauty, not the full orchestral rabble rousing of Beethoven or delicate pianism of Chopin. Not exactly directly translatable to a poster or trailer.
I suspect Bach's place at the top is received rather than recognized, which is not to say he doesn't deserve it. His skill lays in counterpoint and other facets of harmony. His music has structural elegance and ornamental beauty, not the full orchestral rabble rousing of Beethoven or delicate pianism of Chopin. Not exactly directly translatable to a poster or trailer.