It's hard to believe, but when I registered here I was just shy of 14. I'm almost 28. I'm user #306. These forums were very different back in 2004, and attracted a lot of cool people. Those very people have moved on with their lives (as have I).
Forums boomed from 2002 through 2008 because there simple wasn't an alternative. 2009 marked a turning point for many technologies. The financial panic created a "shake out" not just on the Internet, but in the physical world. People looked at budgets and looked at alternative tools.
Communities utilizing forum software will always be around, but general forum software is definitely in a bear market. People use Facebook/twitter/reddit for a range of things that used to be individual websites hosting forums.
I remember iKonboard and vBulletin 2.x, and thinking how cool those things were. Those days are over, but I still reminisce.
From 1998 through 2008, the tech world was "stable": dominated by IE6 and Microsoft. People viewed the Internet through a browser and conversed using forums. From 2009 through probably 2019, we'll look back and notice the world dominated by a more chaotic mix of Apple/Android devices and desktop experiences. There's much more variety on the Internet today.