I definitely notice how uncommitted most of America is to active lifestyle when I go for a run while travelling. Many states, many places, often quite hazardous to get in a couple miles, with no sidewalks, trails, shoulders, or sometimes intersections with no pedestrian signal at all. It is especially irritating when I am somewhere that is a generally newly developed area. I know it costs money, but man it is frustrating.
The streets cost money. Sidewalks etc.? You can get them for 1/10th of that cost. AND you use (aand seal) less space.
I absolutely agree that we need more walkable/bikeable infrastructure, and I advocate for such. But this the cost issue is probably the #1 detractors use whenever a proposition comes forward to expand sidewalks and bike paths. A rather simple two-lane bridge over a small river might cost $10MM, and adding a sidewalk on both sides $1M more. Suddenly there's a very loud camp yelling about a million dollar sidewalk that's only 300 feet long and would 'only' get used by a few hundred each day. So it gets voted down largely on cost, and there's no safe, efficient way for people to get from one side of town to another via foot-power. Never mind that the bridge would service only a few thousand cars per day (less on a dollar-per-car basis) and the problem of more people walking is a chicken-and-egg problem (without safe routes, few will walk or bike, and without walkers or bikers, city councils have a hard time passing infrasturcutre supporting it).
Perhaps the most comicly tragic example is the walk/bike path on the new SF Bay Bridge. The bridge goes from SF to Oakland and has a midpoint on a small island (Yerba Buena), and it cost $6.4B to build. A planned bike path would have connected downtown Oakland (pop 500k) to downtown SF (pop 850k) along a 4 mile route. SF built their half of the bridge with a nice bike path, but Oakland shot it down... because cost. There was a brutal fight in Oakland not to pay the estimated $160MM needed to have 12' wide paths on both sides (remember the bridge cost $6.4B) So now there's a multi-million dollar bike path that goes to a tiny island, instead of connecting the two cities. There's no feasible alternative route, so instead there are 'bike vans' and of course BART (commuter trains) but no way of actually walking from city to city without taking a ~50 mile detour south of the bay.
I'm currently involved in a rather heated town issue (population 5,000) to add a walking path and bikeable shoulder along a 0.9 mile stretch which would connect about 400 homes to our main street. There's no other safe way of walking to the economic center of town from this fairly populated section. It's amazing how many oppose it ... because cost.
The collective attitude is that roads are absolutely vital, but sidewalks and bike paths are a luxury. Once a road is built it almost never gets deleted (and often its expanded) - yet sidewalks are constantly gobbled up because, hey, we need more lanes or more parking. It's a downward spiral towards more vehicles and away from people walking.