> There's literally thousands if not tens of thousands of hosting providers and software packages that offer just that.
But most of them are incredibly confusing and off-putting to the majority of people FB attracts. Most contemporary net citizens don't have a functional mental client-server model such that they would even know they need a thing called hosting, let alone choose a service. And there's no tools that integrate a content feed, personal publishing, threaded comment and events/calenders in a coherent, secure, easy to use way. Most people barely understand that some code runs "in" their browser and some "on a server", or the relationship between the two. It can't be taught in a few minutes (it takes most of us here years to grok the subtleties and there's infinite edge cases).
To really get the whole FB experience, we also need "group-ware" (shared photos, tagging, shared calendar, private chat) with single-click installation, configuration and built-in templated branding.
You're right that all these tools exist, but they're fragmented and take time and knowledge to understand, use and integrate. And most of them are not interoperable.
> Following is through RSS feeds.
RSS is great in principle but all the tools that consume it suck: comment RSS feeds are treated at the same level as content, rather than "of" the content they refer to; most site still use RSS rather than ATOM, so you only get a summary of content; most readers keep you in-app rather than linking to full browsers, so you're trapped in webviews and inflexible, under-featured tools.
Yes, it's all "out there" but none of it matches the speed and comfort of FB.
(coming from someone who no longer has an FB account)