At some point you reach critical mass, where the majority of the population uses the bicycle as at least one of their modes of transportation, after which improvements to bicycle infrastructure are more widely supported and thus more easily made - which then causes more people to use the bicycle, etc.
That's what happened in the Netherlands a couple of decades ago, and the infrastructure now is wonderful and still getting better.
Driving in London and Paris is such a pain in the arse I would never buy one of I had to live there. If I needed a car for a weekend trip I'd just rent one.
I bike everyday to work, and everytime someone ask me "what about the rain" I answer "I know I'm sweet, but fortunately, I'm not made of sugar" it's gets a rolleyes or a laugh, 50/50.
The last stat I've seen in Paris is that if you were to bike to work every day on a 9 to 5 job, then you will encounter rain 17 times per year in average. When that happens, as others said, you can just accept being wet and/or dress appropriately, or take public transport.
Does that take into account the hours when rainfall occurs or how could that number be so low? In a city with an average of 162 days of rainfall/year (according to climate.top, no idea how accurate that is). Apparently Amsterdam has 217 days of rain. Oooff. Been there a few times, can confirm. People still bike.
You see the clouds in the sky? They are made of tiny water droplets. At some point the cloud is saturated and the droplets get too big to stay suspended in the air any longer, so they start falling towards the earth as raindrops. Some may hit a cyclist and either roll off their raincoat or get absorbed by other clothing until they evaporate again, travelling upwards into the clouds and starting their journey all over again.
In most places it actually rains a lot less that you would.think, and often it only rains a small part of the day. I know that when the forecast is for rain often the 30 minutes it takes me to commute are dry.
I commute everyday in a place that has a reputation for being a bit rainy in winter and I get actually wet like 5 times a year.
Rain jacket. Or just a normal coat with hood that's water proof. If it's really coming down waterproof trousers as well that I pack in my rucksack. Rain is really not a problem and I commute every day by bike.
If you have quality rain gear you will stay dry. But also, lots of people choose other transit modes when it rains. I lived in a very bike friendly city and when it rained, the public transit would be packed with people and the roads packed with cars.
In fact, this is a bit of a strange question. Are we assuming that everyone is always going to be biking with no other options? I don’t think anyone is even advocating for that.
On most rainy days you can get quite far with checking rain radar prediction. It often doesn't really matter if i cycle somewhere at 16h30 or 17h00, you look at the radar and try to not get wet :'). Most rain is in short bursts, dry periods between, most cycle trips aren't longer than 20-30 mins. And yeah, sometimes you do get wet. That is okay if you got good gear and if it didn't take you by surprise.
I live in the Pacific Northwest of North America. It rains here a lot. The vast majority of my trips are by bike year round. I tend to find rain jackets and pants cause me to sweat uncomfortably. I usually wear a rain cape. I drape it over my handlebars and it keeps my pants mostly dry and my top completely dry. Once I get where I'm going it's easy to remove and tuck it into my bag.
If I'm just riding to ride I'll wear a merino wool base layer and just get wet. The wool stays warm even when I'm soaked