Is it really true on the internet though? omg.lol could presumably stay "small-appearing" and "quaint" and have millions of users. How could you really tell the difference?
If it were all indexed you could drill down and find people who share your interests, that doesn't necessarily ruin the website, yeah?
The other downside of mass-popularity is that above a certain scale, your community becomes a target. Both for individual bad actors (spammers, vandals, etc.) and for the apex predators of the small community world, commercial interests. Look at Maker Fair transitioning from a relatively niche convention of people showing off their cool stuff they made, and some miscellaneous sponsors and vendors looking to appeal to those people, to an over-commercialized affair with a thousand people trying to sell you a 3D printer, because that's the big moneymaker.
Community norms are what makes spaces worth inhabiting, and they just don't scale well.
Things could continue to be small and niche, we just a way to find them.
I used webcrawler at the very beginning and I'm probably looking that things through rose lenses but I found what I wanted back then. I think back then in some ways it was easier to find your community because SRO and the like wasn't a thing back then.
The years where I found my niche forums benefited me much more than my college days.
Could it possibly preserve that "old web" style of interaction, if it becomes a global phenomenon that everyone uses? Or does this only work as long as it stays a little hidden niche, that most people don't know about, and will never find?
Or in other words - can something feel like "the old web" (which was early adopters and enthusiasts only) - if it's frequented by everyone?
You love the idea of smaller communities - but how can they stay small?