The Egyptian culture was such that they worshiped nature. The strength of nature reaches its fullest and blooms in the Spring season.
This is why HaShem chose to take us out of Egypt during this season; in order to show us that nature has no power, in and of itself, and is merely HaShem’stool in conducting His world, like an ax in the hands of the wood-chopper.
(Biurei HaHaggada)