I know this is just a joke, but I'll reply anyways with a serious attempt to explain it.
Businesses and well--the government, want to be correct and well mannered. Before it was "Happy Holidays" the other religions would be offended. It's like assuming if someone was Christian when he's Jewish. That person could get annoyed by the constant "Merry Christmas" and probably thought of saying ""Happy Hanukkah." Obviously, NO. They would stick with Christmas, instead...
They would do "Happy Holidays!"
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