Why should a business call it a Christmas Party if they do not want to? Are you some sort of authoritarian?
That question is totally non-sensical.
If you are having a party on Martin Luther King Day you don't call, "A Party in Honor of that Black Reverend Assassinated in 1968."
If you have a party dedicated to the 4th of July, you call it a 4th of July Party, not "A Party in Honor of the Day some old white men signed parchment in Philadelphia about 200 years ago."
If you have a party in honor of the sole federal holiday in December, you name the party for that holiday.
You are free to call it anything you want. But what force would ever make you (or anyone) not want to use the proper name for it? Why is the federal holiday on December 25th so difficult for you to accept?