What region are you from, or what specific traditions do you remember that have faded away? What I see is that a lot of local or family traditions have just gradually dissolved because people moved, changed their context, or their kids grew up somewhere else. Things like setting up elaborate nativity scenes, religiously going to midnight mass, the posadas in some places, or even spending entire days gathered with your whole extended family - that used to be way more common, and now people pick and choose which elements they keep. I think part of the shift is also that there's so much Christmas activity available now, social media showing different customs, that people put together their own mix instead of just following what the whole community did.