I don't think that's necessarily true.
I think the root problem is that running & using a forum is too difficult. That is why centralized forums (like you mentioned, reddit and facebook) that handle it for you won out against decentralized forums run by forum members.
Even before facebook/reddit/etc forums tended to live or die by individual effort of one passionate system admin dealing with all the hosting, updates, accounts, and spam until they get fed up and the forum closes because they can't find someone else to take the keys.
For a while there the site was up but not allowing new accounts to be created -- someone was paying the hosting bills but didn't have time to do any admin tasks. Thankfully, someone else stepped up and people post new stuff every day (albeit with banner ads at the top of each page now, which is honestly not too bad)
I'm happy, but it could have gone poof so easily.
But anyone who launches a forum today is competing with the large, metaforum platforms like Reddit and Facebook and Discord.
It's just too difficult to assemble a userbase.
Perhaps the experience is dying, but the wealth of curated information in forums is still there, is still incredibly valuable, and in some cases is still being added to. Here's one example I used extensively recently; it was sent to me by a colleague, since I never could have found it via a search engine.
https://gearspace.com/board/studio-building-acoustics/610173...
I hadn't heard about this, can anyone supply a link for more context?
Is there anything a Cloudflare customer can do to "opt in" to being scraped by other search engine bots?
Amusingly, appending "reddit" to your search is like a pseudo search engine in itself, instructing the search engine to act as a search engine of only a specific domain of information. Almost like we're back to having multiple search engines, and no one knows which one to use...
no, the signal to noise ratio has gone from sufficient to far too low
This is exactly the problem that RSS has been solving since it was created over 20 years ago.
If you have this problem, it means you do not have granular-enough RSS feeds. Per-discussion-thread at minimum.
The root problem is that attention has gone from abundant to scarce, and people already have their habits. That makes it really hard to build a new forum site and attract an audience that's willing to type your URL in every day (and if they don't visit daily, forget about building a viable community). Forum hosts like Facebook and Reddit don't have this problem - you can view your Buy Nothing Group and Moms of Springfield posts interspersed with your feed of friends, or your r/factorio content interspersed with a steady stream of r/AskReddit.
There's also emerging technological barriers. If you don't sign up for CloudFlare, as a new website, you're going to get hosed - but at the same time, CloudFlare makes it basically impossible for any new search engine other than Google to spider the site. Ditto security patches, and keeping software up-to-date. Most people don't want to deal with sysadmin stuff at all, particularly if they're trying to build a community as a hobby. So that pushes people further toward hosted solutions with a turn-key secure software stack, which is Facebook and Reddit.