The financial incentives have become stronger for building walled gardens than a semantically open web. The semantic data has been more useful to giants that monetize it, than to millions of small publishers who are supposed to abide by the rules and maintain it. The issue is even bigger if you are listing valuable goods - from products, to jobs, to real estate/rental listings as a part of your marketplace or business. Aggregators like google can scrape and circumvent you, by taking away your users earlier in the acquisition chain, so why bother giving them your product graph.