This is why we need good public transit on top of good biking infrastructure. The two working together let's you get anywhere a car can go while not taking a lot longer.
You're not wrong, but that's not going to work over the entire country. There's just too much space to cover; the country would go bankrupt trying to provide mass transit everywhere that it's needed. So while this could be, if you could convince people to actually do it, a solution in urban areas, it's never going to work out in the thousands of miles of country and they have the exact same problems. They just have less traffic and more empty space to cross.
We didn't go bankrupt making a car-centric infrastructure, we won't go bankrupt building adequate mass transit and micromobility infrastructure. In fact, we will probably profit greatly in myriad ways.
Acktually a fair few counties in the US have gone bankrupt building car-centric infrastructure, because it's ruinously expensive and doesn't even come close to being covered by the taxation they put on cars. Mass transit and bike infrastructure costs are miniscule in comparison and sometimes even actively gain money.
I just spent a week in Texas in places that had plenty of people living and presumably working close together. The infrastructure is a hellscape of concrete and asphalt and monstrous pickup trucks. It has nothing to do with being a big country and everything to do with culture and policies.
I was specifically addressing people commuting to their job and traveling within their immediate area. That kind of stuff could definitely be covered by biking and better bus/light rail investment without having to go everywhere. The only people who wouldn't be covered by that are people living in the country and they are a minority compared to those living in suburbs or near big cities and could still be served by public transit using park and ride stations if they have to travel to a bigger city. They would just drive to the closest park and ride station and then use the public transit to travel within the metro area. Of course if they're traveling entirely within less populated country areas then public transit won't serve them that well but at that point you can just use cars as a backup. But public transit investments could easily serve the majority of people for their daily travel needs and even if they do have a high cost the economic benefit of making it easier for people to commute to work and to cities for fun day trips will create more economic value over time being a net benefit in the long run.
Get a closer job or move closer to your job if it's a good reliable job. I did and it's fucking wonderful! Riding gets easier and easier as you get stronger and better cardio too.
Took me a long time, a lot of work, and some luck but I can't recommend it enough. Most days I ride my bike or skateboard, but even walking doesn't take long. I only resort to a car if I'm too injured to ride/skate/walk far or the weather makes it too dangerous (which is rare, I've ridden through more storms than I can count lol, icy conditions suck though).
Some lucky few still get to build up an emergency fund, possibly retire, or even become independently wealthy, but yeah, most of us are working class stiffs.