When your trip is 3km you can easily walk. Bicycle commuting is very hard in warmer climates, because you will get sweaty. But motorcycles solve that problem at least. Then you have those cold climates with awful weather, where bicycle commuting is pure misery, compared to riding a car or bus. So it is all very location dependent.
Bike commuting during winter is fine as long as you have the right clothes. I have commuted in a -55F wind chill in perfect comfort. I will concede that it takes a few weeks to calibrate clothing if you're not used to it, but it's not some huge barrier if it's something you're interested in
Snow cover can make it impossible. Frozen rain means you need somewhere to store your wet clothes, and they will not be nice to put on when going back. Somebody who isn't a huge biking freak will prefer the car.
