The highway is already there. It's likely the city was built up around / with it, not the other way around.

I'm all for less cars and more bikes and it is unfortunate the way cities in the US were built. Making wider bike lanes means either making narrower car lanes or wider general vehicle paths to accommodate both, which is fine when there's still enough room to do so. Lots of cities have narrow-ish roads that butt up to sidewalks that butt up to buildings. So, you gotta start removing sidewalks and buildings, or make the roads too narrow for cars / trucks / emergency vehicles, etc., just to have a better bike lane.

Then there is the fact that most small to medium sized (and some even bigger) cities' current public transportation consists of a few busses at best. You have to be in a huge metro for any kind of train or even consistent non-uber taxi service. Also they only run in the city, where most people work, but not many live. It's common to live in the suburbs or a rural area 20 - 50 miles away from the place of work, for various reasons, but currently mostly influenced by cost and existing infrastructure.

Ever tried to bike 50 mi in the rain / snow / 100°F to get to work? Me neither, and it's not just for lack of bikepaths.

There are places making efforts to make cities more walkable and bikeable but it takes time and every solution I see from the fuck cars crowd is, "stop living in the suburbs then, move to a city where everything was built perfectly to be walkable and bikable 150 years ago! And if you can't find one, just destroy all the sidewalks and buildings to accommodate a bike lane and rebuild everything else, I guess. Sell your suburban or country home, change the zoning laws and build a house in an already tightly packed city. Once you've done these very easy things, you can bike all the way across town in 100° weather, or take a bus and be an hour early or 30 minutes late to where you need to be. If that's inconvenient, destroy more buildings or start digging holes and invest in trains!

In the smaller cities like where I'm originally from it's also laugable. There arent enough people or roadways for biking to be dangerous and the only thing to bike to is a gas station at the single flashing red light and you'd have to take 3 dirt roads to get to the pavement. There's no bus, no taxi, no uber, and the nearest town is 30 miles away with nothing in between. But those folks should sell their cars and homes and uproot their entire lives too, because not doing so means they'll drive to a city to survive, and fuck cars.