I have actually wondered about this question quite a bit myself. In theory, if not in practice, we keep Sunday apart from other days. Yes, we attend Mass, but the way in which we spend our day is not the same as the way in which we spend other days. The same is true for Christmas. Because it is both a Holy Day and a secular holiday, we treat it as something special. We gather with friends and family, open gifts, etc. We feast and we celebrate. Because our secular culture and government is so disconnected from the traditional Christian calendar, most Holy Days become just another day to go to mass, which can be a burden for a family to fit in after school or work. Since secular life goes on as usual, it is just another day to so many and the sense of celebration is lost. Maybe we could encourage people to take the day off work and celebrate. Perhaps a parish potluck dinner after an evening Mass? Have a Corpus Christi procession. Bring back the idea of fasting followed by feast days. Try to think of Holy Days of Obligation as great Feast Days in the church, as times of celebration Encourage families to save at least some Christmas gifts to open on Epiphany.