Can someone explain the rationale behind "low" pants?

Took me a while, but I finally found this post, which has stuck with me ever since:

For those of you wondering how they keep their trousers up:

Stringbean 1 (external view).

Stringbean 2 (internal view).

To quote Jeff Foxworthy: “If your parents still drive you to school, you ain’t no gangsta, pull your pants up!”