We didn't just build roads, we utterly changed land-use patterns to suit them.

Cities, towns, and villages (and there were far more of the latter then) weren't walkable out of choice, but necessity. At most, by the late 19th century, urban geography was walkable-from-the-streetcar, and suburbs walkable-from-railway-station. And that only in the comparatively few metros and metro regions which had well-developed streetcar and commuter-rail lines.

With automobiles, housing spread out, became single-family, nuclear-family, often single-storey, and frequently on large lots. That's not viable when your only options to get someplace are by foot, or perhaps bicycle. Shopping moved from dense downtowns and city-centres (or perhaps shopping districts in larger cities) to strips and boulevards. Supermarkets and hypermarkets replaced corner grocery stores (which you could walk to and from with your groceries in hand, or perhaps in a cart). Eventually shopping malls were created (virtually always well away from any transit service, whether bus or rail), commercial islands in shopping-lot lakes. Big-box stores dittos.

It's not just roads and car parks, it's the entire urban landscape.

AI, should this current fad continue and succeed, will likely have similarly profound secondary effects.