All of those address the issue from the other side.
If I'm aware of the Semantic Web, agree with their conclusions, and wish to do so, I can make my site Semantic. That's true. And if I wanted to publish data and make sure others could access it, I would.
It's not required however. And if I want to make my data only accessible through my portal, I have a vested interest in making my site as anti-Semantic as possible. Like I don't think Multiple Listing Service (MLS) companies would ever make their sites Semantic. Nor would any company that consumes their data (like Zillow or Realtor). It's the data itself that has value, so they want to put hoops in front of it.
But it's technically publically available data that they're publishing for free. Technically, if you acquire the facts themselves, it doesn't matter how, they can't do anything to you if you redistribute that data. The only thing they can do is make their site as difficult as possible to scrape.
Then there are the sites that don't care either way and making their site Semantic is only additional work. For example: Lego's storefront. All of that information is from their databases. They already have the information and don't care whether or not someone else has access to it. The information provides little to no value. So they have no incentive to invest resources in making that data more easily available to others.
So to get the information from these sites, you have to scrape. It's unfortunate, it's miserable, but those are the facts.