Probably because the established Winter festivals were hijacked by the Christians who could not account for the whereabouts of their religious leader throughout his formative, and probably spotty and sullen teenage, years.
Oh, and before Christians condemn me to a living hell may I remind you that they also besieged a pagan festival, from the English word Eostre, which is a time for celebrating new beginnings with the coming of the easter bunny [hare] from the festival surrounding the Goddess Eostre.
I was told by a Christian when I was growing up that Easter eggs represented the rolling away of the stone in front of the tomb in which Jesus lay, nothing to do with the origins of Eostre when celebrations centered on the painting for bird eggs.
I prefer the Pagans view that the egg represents the cycle of seasons with the yolk and egg white representing the Sun and the Maiden Goddess respectively.
Whatever your beliefs, may I wish you a Happy Eostre.