[dncornholio]

Because adults don't cycle for exercise, they cycle to get somewhere, preferably not being sweaty and out of breath.

[watwut]

It is exercise. Just not an intensive one. It is way more exercise then driving car.

[dukeyukey]

Sure, but when I'm cycling to work, my primary goal isn't exercise; it's to get to work. So I'm gonna do things that optimise for getting to work in a reasonable state, rather than optimising for exercise.