Ah, come on. You asked for it, didn't you? You wrote "I'm guessing it's a special magic planet with startlingly good weather year-round, without disabled people, where everyone gets to age into spry Euro-oldsters". Of course, such an extreme statement will trigger a reaction from people who actually experience every day what you claim to be impossible. It's not possible in every city and it's not possible for everybody, but it's possible in more places than we think once we accept the idea. One quarter of the Dutch population cycles every day and the number of cycling people (obviously lower than the average) over 65 is actually increasing thanks to better a infrastructure and, of course, e-bikes.
And talking about hot climates: You remember the pictures from South China in the 1970s or 1980s where everybody was cycling because cars were too expensive and public transport was bad? Now everybody has a car and nobody with a sane mind would cycle in China.
If only the world was flat and below the sea level as Holland...
There's various reasons not to use a bike, e.g. the mentioned way too humid/hot weather. However, the high usage is not due to "flat". Netherlands used to have a very high car usage and pretty much no bike usage.
together they represent almost a billion people and the world's biggest cities. Should we ignore them because they're not snowy North American/European cities?
Here in Toronto, Canada, we are building out bike lanes, they are heavily used and it's pretty cheap to dedicate some lanes to bike traffic. They are used ALL year long, even in the snow. Yes, more people use them in the spring, summer, and fall, than in Dec-Feb, but they are used all year long.
Your complaints are not based in reality, either in cost or in usage patterns.
As a European myself this made me laugh hard. Yes, people here have a tendency to see everything in black and white and be really religious about their way of life.
As I said, I'm pro-cycling. Good for you, all you hardy souls. But it is a seriously boneheaded point of view to imagine that cycling is going to be more important as a mode of transport than public transport in most of the world under the conditions that exist now.
There's a large plurality - even in the totally cycle-happy countries - of people that don't ride, and that's a majority past a certain age. These people will get a small benefit (aside from cleaner air and fewer cars on the road, which is nice) from cycling infrastructure. Conversely, a drastic improvement in public transit infrastructure benefits almost everyone - cyclists are pedestrians and transit users some of the time, and they will also benefit from getting cars off the road.
Frankly a lot of folks are confusing their hobby with good public policy.