You're missing my point. Development density doesn't preserve green space. It just puts more people in a smaller space. Protecting green spaces requires actual protections.

This graphic implies that there is a market solution to protecting green spaces. It's suggesting that NIMBYs who oppose high-density zoning are the reason for suburban wastelands. Zoning regulation should prioritize preserving green spaces and public lands, but deregulation is not the fix (as is implied).