Another reason why the franchise began with Episode 4 was because Lucas' first drafts were trying to cram too much into just one film. As much as Lucas intended to make an entire series of “Star Wars” movies to follow A New Hope, even he was fuzzy on the details at the time of the original film's writing.
Handwritten notes on early drafts of the film indicate that “A New Hope” was supposed to be the sixth movie, not the fourth. The numbers changed over the years as Lucas wrote through his numerous drafts, and the first film was released without an episode number after Lucas removed "Episode IV" from the opening crawl at the last minute.