Ironically if everyone lives in low density sprawl for nature, it destroys the same habitat where those wild animals once lived, or where that forest was, and it makes actual nature harder to access for anyone who can't afford or travel to the latest round of exurbia.
Whereas if our cities were denser, there'd be more open space left, that is easier to access, by potentially more people. Density != cramped hovel. And density doesn't mean everyone lives in a highrise. There's points between single family homes on quarter acres and 60 story skyscrapers.
Edit:
I highly encourage you to checkout some examples of cities that saw most of their growth pre-auto:
A wide range of uses, densities, housing prices and modes of transportation (dedicated bike infrastructure, transit, and yes even cars). But the compact development area can leave so much more room for green space, nature preserves, public parks, agriculture, watershed protection. There's even many buildings that have yards - it's just everyone doesn't get their own acre.
I can't say a lot about Leipzig but many german cities were rebuild far more car-centric then they were before. Public transportation, small streets and biking seemed outdated back then. A lot of medieval building were destroyed after 1945 to make room for cars. There's a good german (not subtitled) documentation about this topic [1].
The Nazis had the same attitude before. Cities had to be car-centric, that's why they moved on with the Autobahn and created Volkswagen. The obligation to use bike lanes (Radwegebenutzungspflicht) was issued under the Nazi regime. It was part of the fascist mindset that cities are made of concrete (instead of children playing in parks).
I'm on mobile so unfortunately I have no easy way to provide comparisons. But living in a rust belt city and being familiar with the difference in development patterns, I suspect those numbers are an artifact of the extent of city limits. I'd be happy to look later.
Ie Leipzigs boundary for that number includes the city and undeveloped/agricultural/rural areas in the surrounding metro, where Detroit's number is the developed city limits, excluding the suburbs, exurbs and agricultural places in the metro.
I don't mean to get too bogged down in this point too much. I wanted to point out there are plenty of lessons we can learn from pre-auto cities to make our future more livable.
Yes, I provided you the numbers for city's proper in all cases.
No, Leipzig's boundary for that number does not include their larger Urban Area. Looking at the metropolitan area population of those cities Leipzig is 843,619 while Detroit, the rust belt city you mention, is over 4 million according to OECD.
If you compare the official city limits with the satellite view you will see the developed area containing most of the population is much smaller than the city limits, and you might understand what I am getting at. I think the appropriate measure here would be the weighted density, closer to representing the average density a person there would be surrounded by.
Then why is it easy to live without a car in Leipzig, but (as I learned somewhere else in this thread), impossible in Houston? Density is about the same.
Because even in mid-low density European towns and cities the diversity of land use is greater. Shops, pubs, and parks are permitted to be near housing, as opposed to the US which makes it illegal to have a shop near your house in much of the country.
Whereas if our cities were denser, there'd be more open space left, that is easier to access, by potentially more people. Density != cramped hovel. And density doesn't mean everyone lives in a highrise. There's points between single family homes on quarter acres and 60 story skyscrapers.
Edit: I highly encourage you to checkout some examples of cities that saw most of their growth pre-auto:
Here's my personal favorite - Leipzig Germany, metro population around 1 million: https://www.google.com/maps/place/Leipzig,+Germany/
A wide range of uses, densities, housing prices and modes of transportation (dedicated bike infrastructure, transit, and yes even cars). But the compact development area can leave so much more room for green space, nature preserves, public parks, agriculture, watershed protection. There's even many buildings that have yards - it's just everyone doesn't get their own acre.