>>101 I am currently a student at an American university. My experience regarding frats and sororities is that they are mainly just social clubs for college students. I don't really see how f&s could help students find a job or anything like that. "Why do you need them?" is a good question in my opinion. They really aren't needed, but some students enjoy them. Some of them are rather backward, and f&s are known for occasionally doing immature and irresponsible things. They are known for hosting parties with excessive amounts of alcohol.
At my university, they discourage honor students from joining f&s because statistically, students who join f&s start to make lower grades. Most of the top students are not affiliated with any fraternity or sorority.
Are American students more immature? Well, I can't really say since I don't know much about how mature university students from Japan or other countries are, but it seems likely to me.