Corporations make good villains because Corporations usually are villainous in the real world. The plunder the natural world, exploit workers and corrupt governments all for the sake of profits for a select few.
Corporations are not altruistic or looking out for the best interests of humanity. They do not seek to bring equality or improve the lives of others...its sole purpose is to enrich a select few. History is full of examples of corrupt businessmen doing evil things. Hell corporate greed and banks very nearly drove the world economy over a cliff a few years ago. These same corporations turned to US the people, via our government for help, and then turned around and systematically started screwing consumers...the very people that bailed them out.