The bigger reason why it was a failure is not because it imposes a cost in terms of work on the content creator, it imposes a lack of control on the part of the party that considers themselves the 'owner' of the data. If every webpage that right now is plastered with ads and various junk to get you to subscribe/form a relationship/amplify the content would just be the structured data and a default way to render that data would be present in every browser then most content monetization strategies would fail. Follow the money, not the effort.