Going to the source might help here. When Ray Bradbury was asked in an interview as to his motivation in writing, he offered an insightful answer that can explain much:
I had decided to be a magician well before I decided to be a writer. I was the little boy who would get up on-stage and do magic wearing a fake mustache, which would fall off during the performance. I'm still trying to perform those tricks. Now I do it with writing. Also, writers write because of a need to be loved. I suppose that's greedy, isn't it?
Writing has helped me in other ways. When I started writing seriously, I made the major discovery of my life - that I am right and everybody else is wrong if they disagree with me. What a great thing to learn: Don't listen to anyone else, and always go your own way.
Within this statement, much can be generated. On one hand, when the question is posed as to why Bradbury wrote, a response could be "Because he wanted to display a reality of what could be as opposed to what is." Similar to the "magician" in the carnival of Bradbury's life, Bradbury wanted to write because of the need to construct a reality that enabled him to "perform those tricks."
Another reason that can help to make clear as to why Bradbury wrote could tie into his own sense of self. Bradbury asserts the idea that writing enabled him to be independent of thought and action. Hence, another response as to why Bradbury wrote could be "because he wanted to assert his own individualized voice in a world of growing homogeneity and conformity. In this, one can get inside Bradbury's mind to see the strong connection between writing and independence.