I think because when I started walking, it was equal parts transportation and exercise, and that really planted the deep feeling that I absolutely have to walk all the time. But now that it's an activity I choose to do, I should really only do it on my own terms. And not seeing anything interesting because it's too dark and being miserable because it's too cold has gotten old.
I imagine it'll be beneficial, too. I don't do any strength training and I really should.