1. It really does not become mandatory but it becomes helpful. Some kids succeed in certain environment, for example if a kid is from NY but his family had to move to Mississippi for his high school years, obviously the kid would need to go to NY to get back to the type of environment where he can succeed in as opposed to Mississippi which would be boring to the kid. Going out of state also becomes mandatory when a kid is in a bad situation like lets say an Asian American male living in Montana, he would obviously feel somewhat left out. Also sometimes the kid's parents may have a job that temporarily relocates them to an area opposite of what they grew up in (a family in New Jersey having to move to Texas) so the kid may not like the environment too much and as a result he may want to go out of state just for his benefit. Sometimes going out of state can boost a student's motivation and make him excel academically.
2. Kids have a sense of exploration to them, most kids who have rich families often want to go out of state to explore another culture or because they are often bored with their surroundings (nephew lives in GA and he hates it there, mainly because the state is conservative and there is not a lot to do unless you live in Atlanta). A lot of the times kids who apply to Ivies and get in go out of state because a lot of the places like Harvard and Yale have GREAT financial aid programs so kids really do not have to worry about debt at all.