I believe that it is because we are just
following pagan traditions.
Giving someone you love a gift (or anyone for
that matter) should
not be dictated by any calendar or pagan traditions.
It should come from the heart, be sincere and
be given without expecting
anything in return.
Plus, the best time to give someone a gift is
when they least expect
it, that's when they'll appreciate it the most.
Concerning Santa Claus:
"The origin of this tradition is a fascinating and
deliberate mixture of a bishop-saint, Father Christmas,
Christmas Man, and the Norse mythological god Thor."
Thor is described as "elderly, jolly (though a god of war), with white
hair and beard, friend of the common people, living in the north
land, traveling in the sky in a chariot pulled by goats, and as
god of fire, partial to chimneys and fireplaces"
- Catholic Customs and Traditions: A
Popular Guide, by
Greg Dues (pg. 60-62).