I think the problem is that forums predate what most of the population thinks of as "social media", which is general purpose sites like FB, Insta, X. But I have long held that forums are the original social media, sites where people can meet, converse, share stuff, and so on online. It's just that most are not general purpose hangouts, but built around some kind of theme or focus. So support forums for software or topic-centric boards on things like games or genres of literature or whatever. My site is technically about religion and spirituality but you'd be hard-pressed to tell that sometimes looking at the Latest Posts. They also don't tend to draw broad audiences seeking to just connect with other people, again, due a lot to being focussed rather than general purpose.
But when I look at some of the forums sites I am on, they feel like a social site. My erotic writing site's forums are obviously sex and relationship focused but have lots of general chit chat, too. People meet, become friends, hookup IRL, and we've even had a few weddings over the years (and, sadly, passings). Definitely feels like a social site to me. Ditto my own site but it's so small that the dynamic is different, almost like a neighbourhood or small town where everyone knows your name whereas the writing site is big enough to have multiple smaller communities within it. And then there's my favourite singer's fan site that runs on Circle, where I in Canada hangout with a crowd that's mostly European (she's Dutch and is biggest in her own country and the Nordic countries). And, again, we have friendships forming, people gathering at the singer's gigs, and even an engaged couple who met on the site (one American, one Finnish, they are settling in Finland).
So based on my experience, forums are clearly social media, just tend to be in a specific niche and therefore somewhat overlooked by people not interested in niche spaces.
