Instead, most stacks are designed to enforce a walled garden, from which very little is shareable unless you go through the gateway (the web client app) to some approved destination.
Semantic web and total availability at the personal-computer level, are aspects of OS design I wish had been paid more attention.
Basically what we have now is a very, very expensive system of dumb terminals.
As an example go look at the tags on soundcloud. People tag their songs with whatever they think will get people to take a listen.
There are plenty of trusted sources that would not spam their pages in this way. And if you spam too much, you risk getting dropped from search indexes, directories, links etc. because your source is just not useful.
It's not as if the semweb people weren't aware of the problem, and it's not self-evidently a fatal blow to the idea.