Well, I think there are a few reasons. First, (if u watch the bonus dvd from the 4th movie) it was harrison ford who wanted to do another movie. He got George Lucas and Steven Spielberg together and sed "hey, lets do another movie". Secondly, I think a lot of fans wanted it. They cud hav finished the films on 3, but I think that fans afta 19 years wanted some more. Also, I think our generation wanted an indie too. And also, I think the team did it as a bit of fun. They went off the beaten religous track and went and put aliens in (don't ask me why, I think they could have done betta 2)which kinda seems like they were doing it for a bit of fun. Lastly, I think if it wasn't for indie 4, Shila (is that how you spell it, if not, what i mean is Indie's kid) wouldn't have broken into movies I don't think. I bet there are other reasons too, like George Lucas may want another star wars (e.g, 1 old series of 3, 1 new series of 3). I really hope this helps and good luck with your dissertation!!!