>not to get caught up in nostalgia, but at least the Web used to be comprised of an infinite variety of communities.
But there are more, and more varied, communities on the Web now than there ever have been... the Web has grown, not shrunk, over the years.
Also, even on the "old" web, most people tended to gravitate towards a few sites.
>I'm trying to sort out how we went from a giant, flexible network to a bunch of shittier smaller, isolated networks.
I think for reasons similar to why a country can have a sprawling network of highways and roads connecting lots of cities and small towns, each with its own unique culture and history, but most people will still tend to gravitate towards a few large cities.
Social media sites did a better job of providing the features that people who weren't interested in web development actually wanted, and they're designed to host millions or billions of people, as opposed to smaller forums. In other words, the infrastructure was better.
Most people care more about convenience and functionality than they do the openness of a network, or even where it's hosted. Most people just want a curated network of friends to talk to, share things with and a place to publish content. And whatever negatives the silos might bring, they do make the "networking" part of a social network ridiculously easy. Add network effects to that and I think it's easy to see why they won.
>it feels like the sentiment of the masses acknowledges that these networks are shitty.
People leave these networks for other, similar networks that serve the same needs, or different niche needs, but those needs are still currently better served by centralized networks. They're not rejecting the model itself, just specific implementations.