I have read about and talked with some folks who like to place holidays into their games. Usually, it 's the same holidays or at least the main ones that people celebrate in real life.
Personally, I don't see any good reason to insert a real world holiday (or any other holiday really) into a game. I am not much of a holiday fan to begin with and it's not something I would do, is put a holiday into a game.
That isn't to say I wouldn't put any holiday into a game. I would if it were relevant to the adventure at hand. If it had something major to do with the goings on of the PC's/NPC's it could be interesting.
I can see myself writing an adventure where on "Olaf's Day" the villagers every year celebrate the battle that their then Chieftan Olaf led a victory against their former lords and gained their independence. During this years raucous celebration and using the dark of night and inebriation of people all around, someone crept into the current Chieftan's home and has slain who they thought was the Chieftan sitting in his great chair. only i wasn't. Now the PC's are asked to help find out who it was that slew the Chieftan's oldest son who had been the one sitting in the chair at the time.
See now, here is a useful addition of a holiday in which I can see it being involved in a game. Of course, "Olaf's Day" is a gamed up version of Independence Day. (Not the movie, the holiday)
Outside of being used in such a way though, I wouldn't even think to insert a holiday into a game.