Try driving in -20 on unmaintained roads, and you'll find the same thing as your current statement about biking. The temperature is largely unrelated to the infrastructure's useability
In the example city, Oulu Finland, they see a consistent 22% ridership all the way down to -20C, because they incentivize cycling with well designed and maintained infrastructure.
So what? Maybe it's because those people who only have a bike don't have any other means to get around? You need to look at different reasons before jumping to conclusions.
there exist winter tyres for bikes, that have spikes - ideal for ice
The only answer is radically changing the way we view walking in biking in cities. They are the base of all transportation, and we should treat them as the most important mode of transport for that reason. If we do that, maybe Norway will plow their bike paths. Maybe California will drop their obsession with adding "just 1 more lane" to their freeways. Maybe high-speed rail could become a thing in the US as it is in so much of Europe.
There's no doubt maintained bike paths would make cycling more viable, and in the cities great progress have been made in that respect, from what I can see.
However, for a significant part of the population, that simply isn't much of an option as roads and bicycle paths alike are used by such a small (relatively speaking) number of people that keeping both maintained basically would ensure we all worked with maintaining the network!
From what I googled, Norway's urban population is about 83%, so cycling infrastructure should go a long way.
It also shouldn't be terribly expensive to support rural cycling infrastructure either due to the lack of wear and tear that such infrastructure experienced compared to roads for cars and other vehicles.
Last, cycling, especially in winter, is good if you're able-bodied, but it leaves out people with disabilities, which makes a sizable amount of the population if you take aged people in the mix.
I agree with OP that in general, a good public transportation system is the first step toward better cities with less cars. Bikes can play a role, but can't be the solution for everything.
I grew up with winters occasionally reaching -30°C and the logistics of walking (and cycling) in such an environment are simply time-consuming.
On a bike it takes about as long to get the blood flowing, and once acclimatized the ride can be quite nice.
I've been out riding in -42°C (mostly just to prove I could), and at those temperatures I started running into mechanical problems.
The metal of different components shrank at different rates, and my fork was binding up in the headtube, and the freewheel loosened off such that the ratchets wouldn't always connect with the pawls, causing slippage.
Not if you have a garage or a remote startup function in your car. This is what you're going up against proposing that people cycle in freezing temperatures.
> On a bike it takes about as long to get the blood flowing, and once acclimatized the ride can be quite nice.
That's the same as using the outdoor pool in an aquapark in winter, which I enjoy doing because... there's almost no one there at that time of the year!
We have a climate crisis, an obesity crisis, and also a mental health crisis, and bikes serve to alleviate all those things.
Stuff like morals and good citizenship: people just don't seem to value these things anymore. That's tragic, and also catastrophic.