Relays, AppViews, etc don't just index information. Blogs and their interactions are generally slow-moving, but social media is direct and responsive. Notifications and fast interactions are key. So search engines, yes, but we should also think of these components of doing much more.
But let's stay on this blog/search engine analogy for a while before we unpack what it means on a *technical* level, which is interesting. Let's analyze for the moment from a power dynamics level.
Building a web search engine is actually pretty easy these days, you can do so with off-the-shelf tools. And yet there are only a couple of search engines *really*, Google and Bing (DDG mostly uses Bing). And yet the information is right there. *Anyone* could run their own engine. Why don't they?