Very well written introduction to some of the problems with semantic web dev.
Personally I think the reason it died was there were no obvious commercial applications. There are of course commercial applications, but not in a way that people realize what they're using is semantic web. Of all the 'note keepers' and 'knowledge bases' out there, none of them are semantic web. Thus it has languished in academia and a few niche industries in backend products, or as hidden layers, ex. Wikipedia. Because there wasn't something we could stare at and go "I am using the semantic web right now", there was no hype, and no hype means no development.
Very hard to make a business case because for the reasons you mentioned + the costs are very front-loaded because ontologies are so damn hard to build, even for very well-contained problems. Without a clear payoff, why bother
Yes because that is about formalizing all human thought and knowledge. In principle that has nothing to do with computers and is something everybody working in science and humanities has been always trying to do starting with Socrates or was it Pythagoras. It is about "building theories".
Now computers can help in that of course but it doesn't really make it easy to create a consistent stable "theory of everything". As we used to say "garbage in garbage out".
Personally I think the reason it died was there were no obvious commercial applications. There are of course commercial applications, but not in a way that people realize what they're using is semantic web. Of all the 'note keepers' and 'knowledge bases' out there, none of them are semantic web. Thus it has languished in academia and a few niche industries in backend products, or as hidden layers, ex. Wikipedia. Because there wasn't something we could stare at and go "I am using the semantic web right now", there was no hype, and no hype means no development.