Adopting a polyphasic sleep pattern only really works if you don't have to do things like work or school.
also we don't really live in a 24-hour society so unless you are someone who is working hard on particular projects which demand a lot of time and attention, there isn't really much incentive to spend large portions of the nocturnal hours awake over, say, planning and keeping active during the time you are awake in the day.
if our society was more like the Japanese urban model, where day and night are just different times of the day, everything is open until very late and open very early (or else never closes) and people work as many hours as they can fit in, i could see it being more productive then.