Consolidation on narrow themes is ensured by our reliance on query->answer search engines.
If you think about the shape of the web at the time Google introduced PageRank, It was a huge graph of content connected by fine-grained related interests. It got that way by people doing the work of drawing those relations; and it's a lot of work, given that the number of potential relations is essentially proportional to the square of all existing content. All of the interesting information is in the edges of that graph.
Who's doing that work now? PageRank incentivized people to trade links for the purpose of ranking higher on Google. People became reliant on the convenience of Google to find anything to the point that if you don't rank on Google, you don't exist. People who created content for the sake of the content, and interacting for the sake of interaction, stopped doing it because why waste time yelling into the void? People who felt like they were providing for the community by hosting these sites had no reason to continue. Without people creating, exploring, interacting, and relating content based on pure interests, there's nobody doing the hard work to organize the web in a way that makes it traversable.
We're entirely reliant on platforms showing us the content they want us to see, and what they want above all else is for users to be predictable. If your interests and behaviors are too nuanced for the algorithms to get a handle on, you can't be categorized, packaged, and sold to advertisers with some expected conversion rate.
At this point in time, most of the people who spend time on the internet have never even experienced anything different, and those who have barely remember. If your business relies on their attention, what good is a website going to do you? Your income relies on appealing to social media algorithms, not gaining the trust of the people who used to shape the web.