I actually strongly disagree with this. This is how many social media sites have failed.
I don't know if alternative social media can ever scale as large as Reddit. Tildes.net and Lemmy both have similar activity to Hacker News and I'd consider them both "successful."
The truth is that Reddit, Instagram, Facebook, etc are not websites used to drive connections between human beings; they're media machines meant to create ad distribution channels. And that's what users want.
When someone uses Instagram, they don't want to see their friends vacation photos - they want to see Cardi Bs latest post. Meta attaches ads to that interaction and that's how they drive revenue.
When someone uses Reddit, they aren't seeing what their neighbor has to say - they're consuming a long flowing rage bait story or a web comic. Sure, there are smaller, niche communities but that isn't the bulk of the site traffic.
And, honestly, content is addictive. I'm personally not on Reddit to make friends or deepen my connection with other humans. I'm there to scroll through memes and cat pictures.
I think that smaller social media sites fail because they don't emphasize media generation and distribution. That reframing still presents difficult problems to solve but I feel like that simple perspective pivot helps with growth. Like, if you wanted to take the "OG" Reddit approach to bootstrapping a social media site you could just programatically generate massive amounts of fake content. Rage bait stories, product placement, etc. Just firehose as much media to drive engagement until you get actual human beings to take part.
That is is growth is what you want. It's arguable whether hyperscaled social media platforms actually make society better or individuals happier.