It does sort of make me wonder what community need Reddit fulfills - discoverability/searchability? Single login? - because it's sort of a weird halfway house between forums (differing in that not searching, and duplicating an old thread is somewhat necessarily okay) and chat.
1. Relatively easy to create a subforum.
2. Someplace you can post [pseudo]anonymously.
3. Has a critical mass of people.
4. Is accessible to anyone on the web.
There's a subreddit for all sorts of topics, and if there isn't one, it's fairly easy to just start one. You don't have to deal with setting up forum software or paying someone for it, and if you want to you can create a post with a pseudoanonymous throwaway account. It's really easy to come and go, and there's enough moderation that it hasn't in general devolved into a *chan-style environment, but not so much it's alienating.
Pseudoanonymity is maybe underappreciated in social networking I think. It's really a key feature. Once you reach some mainstream critical mass, having that feature really moves things along.
If you could replicate those four things in a decentralized way, it might take off. But there's a chicken-and-egg issue with network effects.
What I mean is, Reddit to me seems a step closer to something like Discord. And yet Discord is apparently still necessary; so why Reddit, and not traditional forum + Discord?
I added 'single login' as an after thought, because it didn't occur to me at first, but I think that must be a big reason. But even then there's Discourse, with not single but much easier and OAuth (signup/)login.
The default state of a Discord is hidden. You need an invite link to join a "server." It is set up in a way that your meeting point is outside of Discord, usually real life, at least per their marketing material (irl groups are probably the most value in terms of ad revenue).
Reddit has a standardized layout, you don't have to learn a new interface. It has single sign on, so you don't have to create a new account to participate in a community (low friction) and it has the people. Also, it has the voting concept which helps filter content so you aren't having to do that yourself by scanning topics.
A "classic forum" trying to get off the ground would be competing with all of that. You could also argue, "why Discord? Why not IRC?" for much the same reasons.
Yes, that is exactly what I suggested in comment previous to (up-thread of) the one you replied to.
As I said there, there is also Discourse, with only slightly more multi-community friction really, making it far easier and more standardised to do initial sign-up.
