I have asked myself the same question. It was founded in 2005 by a couple students and became an internet success very quickly. Maybe it was because there was a niche for this type of site at the time but it now has millions of visitors each month.
It is loaded with information and I have found some of my favourite sites through it. If I'm looking for something new or if I have a problem that I can't solve Reddit is the answer. It attracts people from all over the world and even site owners will answer questions that members ask to try and help them out. I find some of the information is a little out of date but it still makes an interesting read.
I wonder if those students realised when they began just how popular the site would become. They should be proud.