Vernalisation just means that plants require a period of cold winter temperatures to trigger the reproduction process...
This means that the plant is reproducing and flowering during the period just after winter, i.e. spring. It's warmer, there are more animals and bird species around to ensure the spread of pollen, etc.
I also suppose that it is a natural adaptive advantage to NEED the winter period in order to reproduce, so that plants living in cold environments can survive.
It's similar to how gum trees need the extreme heat to trigger pods to open- they have adapted to the fires and heat that would kill off any other plant.