This is the correct answer. It's why people look for chocolate eggs left by a rabbit when they are supposedly celebrating the death and resurrection of the son of god, or why kids get gifts from a old obese man when they are supposedly celebrating the birth of that same godly spawn - rationalisations were innested on activities that people already enjoyed for one reason or another.
People turn things into traditions simply because they like doing them with some fixed cadence. The rationalisations tend to flow in later.
In Poland, this makes Home Alone and Die Hard both Christmas movies. Ever since I was a kid, I remember both being on TV during Christmas days. Hell, people actually made quite a large uproar couple years ago, when the TV station showing Home Alone decided not to show it on Christmas, and AFAIR they eventually changed the programming to keep it.
If it becomes one more of the christmas-centric traditions, then it becomes a christmas movie.