I will give my uninformed opinion since we can generalize it to the message boards.
The '10s have been a bad time for forums. Reddit was around during 2008, but it wasn't a huge competitor, and chat services such as AIM, Skype, and IRC have been around and have never supplanted message boards. What really supplanted message boards was the innovation of smart phones.
Smart phones were a technological innovation that changed the way we lived. Rather than shitty mobile web browsers that looked like unfinished read-only '80s websites, you could actually look at a web page directly on your phone. So, a person didn't need to be on their computer to actually look at a web page but could actually look at their internet pages on the go. This was a very convenient event for web developers everywhere and for users. You could go one your sppf or your bmgf while on the train or at school. At this time, Facebook, YouTube, and Reddit were growing, but message boards still had their place.
The problem is that forums didn't really innovate from there whereas social media platforms that are currently large did. Releasing mobile apps was such a game-changer for people. Reddit released a third-party built app in 2014, Facebook had a mobile version since 2007 but released their app in 2009 and polished it by 2012, and YouTube by 2012 had theirs out. This gave users the convenience of not even needing to go on their browser to go to websites but just downloading an app.
Another thing is that these social media platforms (not Reddit really, which is a small potato) expanded to consolidate users to using their products in a type of ecosystem where if you use one company's services then you'd e able to get other things. It started with sites just offering different activities on their platform (Facebook games or Facebook dating for example) and has now moved to either absorbing other companies (eg Facebook buying WhatsApp and Instagram and then merging the services) to bundling their services (eg Apple+, Amazon Prime) into ecosystems.
With this type of convenience, it's no wonder that people would move on to more convenient options. Forums simply stagnated with outdated technology that couldn't compete in the market. Not to mention that these social media platforms incentivized celebrities and other famous individuals to use them for visibility, which only incentivized advertisers and users to flock to the products.
A recent survey was published here:
Big social media has taken a hit even greater than scum companies such as Amazon because of many issues: privacy, censorship, etc. What might revitalize a deconsolidation of social media might be the current trend against these companies that is driven by right-wing actors. Notice that hardware and general software companies are mostly fine (unless they're Chinese), but social media giants are taking hits to their popularity. The current social media consolidation may be outdated in a decade and replaced with something newer as technology advances. We'll see how it goes.
