Yeah, I think the aspect of mystery is what’s important - knowing it does something special on christmas, but also that it does something on new year’s eve is like… well, what ELSE does it do? And leads you to want to experiment. With seasonal DLC in MMOs, you know exactly what you’re getting and for how long you’re getting it.
With christmas nights, whatever you find feels like “wow, look what I found!” I mean even if you look it up on gamefaqs or whatever it still feels like “hmm, I wonder what this combination at this time of day will yield.” The possibility space is not actually that vast, but the potential it occupies in your mind is quite large!