> Using Reddit, a single forum about Ubuntu (/r/Ubuntu) would cost around $5 a month on DO for someone to host themselves. Using something like BBForum or something similar would not require much in the way of maintenance.

For that $5 however, you're not getting DDoS and spam protection.

> The point I am making is that all this stuff existed long before the big tech platforms. It can easily exist without them too. They are not actually providing anything of any worth that couldn't easily be found elsewhere (well, used to be found elsewhere!).

There's a reason ye olde ways of communication are pretty much dead, replaced by centralized platforms... dealing with the obvious noise of hackers, script-kiddies, spammers, piracy and CSAM is the biggest IMO. As a moderator of a sub-reddit, you don't have to deal with any of that, you are free to focus on moderating content - and unlike mailing lists, usenet or classic forums the users can perform self-moderation by downvoting, further lessening your load.