1. Not everyone goes to Israel. There are plenty of non-Israel options.
2. Israel is more fun than going to a local yeshiva. Kids that age in almost all cultures like to get away from home. It has nothing to do with being more mature.
3. Israel is typically cheaper than going to non-Israeli student and staying in a dorm.
4. Eretz Yisrael is our homeland, and is a great place to visit (as long as you ignore its somehwat annoying government and rowdy neighbors)