Even here in Germany many people ride their bikes all year around.

Even here in Minneapolis many people ride their bikes all year round, with fewer riding when it is extremely cold or snowy, but coming back out when it warms up just a little.

What’s interesting to me about Minneapolis and other northern cities where there are a lot of cyclists is that they very often have far more people riding to commute or do other practical tasks than any number of other cities with much milder climates. In the American south, where you never see snow, commuter cyclists are practically nonexistent. Obviously there is a climate challenge of a different sort, but not insurmountable ones and not all year round.

Citation needed, I know. There’s a relevant article about this phenomenon out there somewhere, if I can find it I’ll post a link.

Heat is way worse than cold. Many people can't do harder physical activities once it's around 30 degrees Celsius and/or humid because they would pass out (me included, when it's over 28, I just drive everywhere because I can't stand it outside). The idea that someone in their full health would force me to bike onto the steep hill where I live (and 18 km away from my workplace) is extremely unsettling to me. Public transport is not an option - it takes 50 minutes that way (while just 12 min by car) and the buses and trams are constantly overcrowded, late (or don't arrive at all) - and you definitely can't transport a server (or groceries for a 5-member family) that way.

Riding on the rare occasions there's snow on the ground in London is great. Assuming you can avoid snow in your chain (which causes it to skip the sprockets), the roads are empty - no cars, no busses, it's lovely.

You've got it bass-ackwards: biking becomes more difficult the closer you are to the equator. You can always add insulation to protect from cold, but you can't go much further than a singlet+shorts in case of heat.