I'm not sure that the rate of acceptance of foreign transfer students is low, as opposed to just the total number being low. I would think your status (CA resident studying abroad) would be highly desirable, assuming your grades are very good.
I'm not sure about the limited housing idea, since USC allows transfers with any number of college credits. Aren't sophomores as likely to stay in dorms as freshmen? If they are limiting the number of freshmen to hold space for transfers, I think it is a great idea to boost diversity and provide a 'second chance' for kids who might not otherwise be able to prove themselves by the end of high school.