The people who held sway in the urban planning and home building industries in the 1940s/50s intentionally did a few things:

- encouraged suburban development to either have no sidewalks, or to only have "internal" sidewalks (between houses), with no sidewalk between the homes being built and the nearby businesses

- all private lots were wall-to-wall (fence to fence), meaning no cut-through trails between properties for pedestrians; the means if you look out the window and see a neighbor's house you need to visit over on the next street, there is no foot path between any of the homes between you and them, you have to walk all the way around the entire cluster of houses and you have to walk in the street

- most new homes being built, were built away from the city, and it was [details] something that has come to be known as "exclusionary zoning". All residential properties are put together, all businesses are put together in a different place, no mix/match even for smaller businesses. Most home-based businesses were against the law.

- the car was viewed / treated as the savior, all other forms of transportation were now low-class or the unnecessary baggage of "old fashioned times"

- most cities passed laws that sidewalks are the responsibility of each property owner. A developer or homebuilder COULD build a sidewalk, but did not have to. And if they did, it was on them to maintain it. Some did, some did not. Here is one example of one such where homes built 70 years ago did (and did not) build: Document (1920×1080), the city is still offering to build on the missing gaps even all this time later.

- streets and intersections are designed for what is called "LOS" or "Level of Service", this method of measuring assumes that everyone will have (and use) a car for all trips, no matter how short, and streets are designed with that in mind. This is why the crosswalk in my example below may only allow for thirty-seconds to cross the highway, just as one example. The only goal that mattered if you were a traffic engineer in the 1960s - 2000s was "How many cars can clear this intersection per hour, and per day?"

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Here is an example of a house at the end of a street, literally has a trail across the street. Applebee's Grill + Bar to 3000 Glen Oak Ave N, Clearwater, FL 33759 - Google Maps

The trail goes through a park, which is nice! But the restaurants and shops are only 700 meters away, right? Is there a trail over that way, too? Or some quiet streets?

No, the trail doesn't connect to the housing blocks between you and the restaurants/shops, so you can't cut through a nearby development to get there. You have to walk away from the destination, wind through the neighborhood, then you are out on the "main" road, but that main road is six traffic lanes (plus turn lanes) and very fast traffic. You have to cross several side streets, only one with a stoplight/signal. There do appear to be sidewalks the entire way, but that is very unusual. Usually sidewalks start, stop, and switch sides with no obvious reason.

To get to the restaurant I pinned, you have to cross that highway. In this instance you could wind through your neighborhood and follow "this" side of the highway to cross at the light, but there are seven lanes at that point plus a center median; and the center median does not extend to the crosswalk (meaning there is no place to "hide" in the middle if the light changes while you are crossing). You just have to run, sometimes literally. God forbid you have a three-year-old or a grandmother with a cane, or you're in a wheelchair with limited speed. If the stoplight/signal is only 30 seconds long, you better be averaging only three seconds per lane.

By the time you get there, you've walked 1.5km for a 700 meter distance and risked your life to cross the highway.

Speeds on that road are posted at 45mph (72km), though traffic usually moves faster than that.

And there are places with even longer routes for shorter distances, a 2:1 ratio is pretty average. Many do not have a sidewalk along the highway (this one is unusual in that regard), or a sidewalk only on one side. In others the signal/stoplights are very far apart (note that this is the only one in that entire distance). If you wanted to go to this event center instead, which is closer to your house than the restaurant? You either cross the highway with no traffic signal, or you walk even farther than you did to get to the restaurant despite it being much closer to you (so you can use either the signal you did for the restaurant walk, or the pedestrian bridge at the park just south of there). Kapok Special Events to 3000 Glen Oak Ave N, Clearwater, FL 33759 - Google Maps

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Like I said, the people doing the planning and politics of "how to design" with cars in mind absolutely had rubbish ideas about racism, classism, and "car is status and it's the only way!", and they created these sorts of spaces that require a car unless you have a suicide wish as a way to "filter" for the sorts of people and attitudes they themselves had.

There were some protests at the time, similar to what would happen in the Netherlands 20 years later, but the timing in the course of history was on the side of the developers at that point and this was really sort of the "first" iteration of building for just the car. The protestors lost, and by the time it was realized what the downstream consequences were, no one was wanting to spend the billions to completely flatten and then re-build the millions of square kilometers (miles) of new development.

Here is a comparison picture of a downtown in the 1970s v. today, you can see how much land had to be flattened in order to put in the parking. (Downtown was not mostly empty in the 1910s, but I don't have that image on hand): Reddit - https://external-preview.redd.it/denver-parking-lots-1970s-vs-today-v0-FEoN3IOm6NCsgFvY6BTT04YUFQ4vrMmlADDb-G3wMxQ.jpg?auto=webp&s=57a1c7afb7f5b2c676dc964f06a41d02cc596b95

And that last picture also points to changes being made in the current era -- traffic engineers and city planners are starting to retrofit a lot of streets with bus-only lanes, adding trains, adding bike/walk options (such as in the restaurant example, with sidewalks along the highway), adding cut-through trails that I mentioned, etc. but it's going to take years more to completely undo the damage we did in just those thirty or forty years following WWII.