Besides climate, hobbies and your profession are other factors. Though I live in the desert and probably could get away with sandals all year round, I do enough work in the garage and general screwing around in the desert that my feet would be horribly mutilated if I did so. I imagine warehouse, steel, construction (etc) workers would have some qualms about wearing sandals to work.
Plus I find all the crap that accumulates on the soles of sandal-wearers rather unappealing. 'Bout the only time I wear sandals is when I plan on getting wet (rain notwithstanding.)