There is another practical reality that separates the US from Europe specifically with respect to walkability. The US has much more extreme weather in many places. What would be called severe heat or cold in much of Europe, which I've suffered through for the week if need be, is normal weather in many parts of the US for several months on end. You need alternative transportation for those extended periods.

Few people enjoy being outside in a tropical swamp with a double-digit UV index. Same with the extreme cold that you get in the central US far from the ocean.

I live in Seattle, where many people walk everywhere all year (myself included), no car needed. But that is because the weather is perfect for that kind of thing, being 5-25°C with limited precipitation virtually the entire year. If I lived in Houston, for example, I would be driving in the summer regardless of how walkable the city is.