What a lot of folks don't realize is that the Semantic Web was poised to be a P2P and distributed web. Your forum post would be marked up in a schema that other client-side "forum software" could import and understand. You could sign your comments, share them, grow your network in a distributed fashion. For all kinds of applications. Save recipes in a catalog, aggregate contacts, you name it.

Ontologies were centrally published (and had URLs when not - "URIs/URNs are cool"), so it was easy to understand data models. The entity name was the location was the definition. Ridiculously clever.

Furthermore, HTML was headed back to its "markup" / "document" roots. It focused around meaning and information conveyance, where applications could be layered on top. Almost more like JSON, but universally accessible and non-proprietary, and with a built in UI for structured traversal.

Remember CSS Zen Garden? That was from a time where documents were treated as information, not thick web applications, and the CSS and Javascript were an ethereal cloak. The Semantic Web folks concurrently worked on making it so that HTML wasn't just "a soup of tags for layout", so that it wasn't just browsers that would understand and present it. RSS was one such first step. People were starting to mark up a lot of other things. Authorship and consumption tools were starting to arise.

The reason this grand utopia didn't happen was that this wave of innovation coincided with the rise of VC-fueled tech startups. Google, Facebook. The walled gardens. As more people got on the internet (it was previously just us nerds running Linux, IRC, and Bittorrent), focus shifted and concentrated into the platforms. Due to the ease of Facebook and the fact that your non-tech friends were there, people not only stopped publishing, but they stopped innovating in this space entirely. There are a few holdouts, but it's nothing like it once was. (No claims of "you can still do this" will bring back the palpable energy of that day.)

Google later delivered HTML5, which "saved us" from XHTML's strictness. Unfortunately this also strongly deemphasized the semantic layer and made people think of HTML as more of a GUI / Application design language. If we'd exchanged schemas and semantic data instead, we could have written desktop apps and sharable browser extensions to parse the documents. Natively save, bookmark, index, and share. But now we have SPAs and React.

It's also worth mentioning that semantic data would have made the search problem easier and more accessible. If you could trust the author (through signing), then you could quickly build a searchable database of facts and articles. There was benefit for Google in having this problem remain hard. Only they had the infrastructure and wherewithal to deal with the unstructured mess and web of spammers. And there's a lot of money in that moat.

In abandoning the Semantic Web, we found a local optima. It worked out great for a handful of billionaires and many, many shareholders and early engineers. It was indeed faster and easier to build for the more constrained sandboxiness of platforms, and it probably got more people online faster. But it's a far less robust system that falls well short of the vision we once had.