I have always thought that Christmas was about celebrating the birth of Jesus Christ, but apparently he wasn't even born in December which has made me confused about why all Christians celebrate Christmas. I also read somewhere that garland, wreaths, mistletoe, holly, evergreen trees, yule logs, and gift-giving have Pagan roots which is ignored by most Christians. I have had a hard time with finding something about the evolution of Christmas and how it got so widely accepted by Christianity.
See the answer by u/KiwiHellenist to this question about Pagan traditions in modern Christmas
Others have linked previous answers that address Christmas traditions. As for the dating of Christmas, I answered a similar question around this time last year and included links to other answers that have tackled the topic.
As others have indicated, this a seasonal question with answers that discuss how there is no evidence that Christmas traditions are for the most part recent and cannot be tied to anything from pre-conversion Europe.
That said, (taken from a caveat I provided to other answers a few days ago), there is a natural frustration on the part of enthusiasts of "pagan roots." There was clearly an old fascination with the importance of the winter solstice: it finds its expression in prehistoric stone alignments, in the Roman Saturnalia, and what little we know of pre-conversion Northern European Yule celebrations. With all of this, it is all too easy to see survivors in early modern Christmas traditions.
Coincidentally, it is all too easy for historians rightly to shoot down attempts to connect the dots between "pagan roots" and these early modern traditions. So what is going on here?
Folklore is in constant change, but sometimes there is also continuity in the midst of that change. Europe is far enough to the north that its residents have consistently seen significance in the darkest period of the year, and it is natural to imagine (and occasionally to demonstrate) that they acknowledged the importance of this time with traditions. They inherited traditions from previous generations, and those traditions changed through time as they passed on to the next generations.
What remained a constant was and has been the fascination with this time. It appears that many European cultures consistently saw this as a time when the veil between the world and the next became thin, when dead ancestors, spirits of various sorts, or whatever, could enter the home and needed to be avoided and/or placated.
Are these traditions tied together historically? Certainly not in a way that can be demonstrated with historical method, and for the most part, that should be and is the end of the discussion as far as the discipline of history is concerned.
Are these traditions tied together thematically? That leads us to a realm with vague, unverifiable answers. It is easy to answer yes - and that is certainly the way I see it. One can imagine changing traditions mutating so completely that as one generation passed them on to the next that there is, in fact, some continuity. But this cannot be proven. None of that is not "doing" history. This question and its intuitive answer is, I believe, the source of the frustration expressed here.