It was more than just another project. I never would have accepted it had it been just a money proposition. But I do somewhat prefer doing my own original fiction to writing in the Star Wars universe. Well, I got the word during a phone call from my agent. When talking to my agent, I always force myself to remain calm and sober.
Some people really identify with specific characters.
Some have an attachment to, even if they don't recognize it intellectually, the cultural assumptions on which Lucas built his script. Some people were blown away by the fact that extremely sophisticated SF vistas could now be filmed realistically. Some people just found the universe a compelling one. I tend to fall into the last two categories. Write your own original works first.