I believe the main driver of success was product development. This is because, in addition to the reasons stated above, product development was also the root cause of every other change. Product development firstly allowed for centralized distribution, which was not possible with the old formula. Second, it allowed centralized manufacturing because plant location became less important. Third, the change to the formula was exciting and new, which helped drive funding. Finally, the Twinkies were explicitly marketed on "lasting forever," a direct result of product development.