I would say part of it is culture and fun. They grew up with it, it's fun, and even the unsaved can get behind some the warm and fuzzy values like family that are part of the traditions. There's also the materialism aspect of presents.
Of course, there is an upside to the cultural inertia. Like with Easter, many people who normally wouldn't care will make a trip to a church sermon as a special occasion thing. Many won't come again until Easter, but it's still a good possible 'hook' for the Holy Spirit to do its work through.