The thing being ignored is the massive productivity increases that will happen with AI. Where 10 acres would previously produce 1000 bushels, AI will make it 5,000. Where a factory could normally produce 1,000 cars a month, now it will be double or more. Stuff like that. Material goods will be plentiful, and plentiful means cheap, hence the post-scarcity world. Yes, many problems/issues flow from this, but many benefits also.
All families in the United States could live on one acre a piece in less than 10% of the land area (not including Alaska).