Copenhagen in the summer is about 75° F and fairly low humidity. Ok for a comfortable cycle to work. Many midwest American cities reach mid 90's temp and high humidity. If you cycle to work you'll need a shower when you get there, assuming you don't get heatstroke on the way.
Cycling is not viable transportation in many areas, and you can't cherry pick a place like Copenhagen and use that to support a claim that it works everywhere.
Where I live, the weather is amenable to cycling maybe 4 months out of the year, and it's far faster to drive than cycle in any case.
I live in the Midwest US (specifically southern Wisconsin). Our temperature generally ranges from maybe -10 to +90 F or roughly -20 to +30 C, with occasional weeks that go beyond this range.
I commute to work by bike throughout the year. Admittedly, I avoid the worst of the summer heat by adjusting my work hours so I leave for work before it gets too hot. Also, I'm kind of a freak in the sense that I don't sweat a lot.
If you're curious about this, the weather history feature for Weather Underground will produce nice graphs for most places worldwide.
The midwest has some of the coldest winters of any region of the US because it doesn't have the ocean nearby to moderate temperatures. Most of the midwest would spend most or all of December, January and February well below 40 degrees.
Commuting by bike is still doable in the 90s. You need a rack/basket on your bike so you don't have anything on your back, and you can't ride hard so you don't sweat as much.
Cycling is not viable transportation in many areas, and you can't cherry pick a place like Copenhagen and use that to support a claim that it works everywhere.
Where I live, the weather is amenable to cycling maybe 4 months out of the year, and it's far faster to drive than cycle in any case.