It isn't that difficult to see why Reddit has become so popular and successful over the years. Reddit was founded in 2005, it might sound like a short time, but it's actually a long time in relationships to the internet and social media. Although Google was officially launched in 1998, it's other major services like Gmail got launched in 2004, a year before Reddit. Facebook too was launched in 2004. Judging from this, you'd agree that Reddit has come along way and is also a media giant like the instances mentioned earlier.
Reddit is a forum where you can find almost every information you seek. This is because of user activities which has been going on since 2005. This was a period where sites like Reddit were rarely available as we see today. I guess we can refer to Reddit as a pioneer in it's line of operations. And unlike other early forums, Reddit stood it's ground and continue to strive regardless of any issues they might have faced at the start.