I have this too, Sarah. I subconsciously need to feel I'm making brisk progress, even if I'm going nowhere. But I'm still constantly observing - even fast walking is slow enough to participate in the wider world and perceive its details.

I think the pace and rhythm are important to achieve the easeful physiological state that walking gives, as the foundations for mental reflection or meditation. With slow strolling you can hear your body's engine stutter, like a car in the wrong gear, instead of smoothly gliding along.