Forums are for writing things that deserve to be written, because they archive for later reading that which deserves to be read. No one remembers what they wrote on Twitter or Facetube two days ago, let alone years back when they need to find that one nugget of advice they vaguely recall. Because there's never anything important or interesting posted; just eye-grabby junk.
You also sure as heck can't actually explain something technical in a three line text morsel.
People's attention spans are getting shorter (somehow) and text that doesn't dance around or pop up constantly simply isn't entertaining enough for those wishing to merely consume information (which is fine and dandy, but forums have always been much more rewarding when you bother to get involved)
I personally think that forums with a mission have the best chance at survival, rather than those that are simply 'fora with a focus'. THR quickly became boring for me when I first got into guns, since the discussions here just simply aren't that technical or interesting beyond basic information (nothing wrong with that, as it's more accessible to non-nerds), but now that I am more interested in the legal, political, and philosophical aspects of firearms ownership, there are enough novel opinions on those areas to keep me entertained & sharing what I've managed to learn. I'm glad THR has advocacy as a strong, secondary focus to equipment concerns. When a forum loses its focus, things go all haywire and garden weeds (zombies, conspiracies, prepping, bigotry/flaming, political hackery, dangerous/illegal stuff, general craziness) start popping up all over and the few remaining normal people are scared off. Lot of the old gun building sites went that way, it seems.
There's a life cycle for all things, and something like a forum that's typically maintained by a scant few people is certainly no exception.
TCB