Why then is Christmas day a holiday?
Over here Christmas is more of a secular holiday. We see way more Santa's, Frosties, and things like that than we do Nativity scenes.
Most of our holidays are not religious based at all.
January 1st (New Year's Day)
January 15th (or 3rd Monday in January -Martin Luther King Jr. Day)
February 21st (or 3rd Monday in February - President's Day To honor George Washington & Abe Lincoln)
May 31st (or last Monday in May - Memorial Day - to honor those we lost during war)
July 4th (Independence Day - When USA became an independent nation)
August (last Monday in August - Labor Day - Honor the American worker)
October 21st (or 3rd Monday in October - Columbus Day - to honor the man who "discovered" America)
November 11th (Veteran's Day - to honor those who served in our military)
November 24th (or the 3rd Thursday in November - Thanksgiving Day - to honor the original settlers of American colonies)
December 25th (Christmas Day - celebrate the birth of Christ for those who follow Christianity, for those who don't, to celebrate the arrival of Santa)
One must remember that this country was predominantly Christian, so that is why we close everything for Christmas. If that was tried to be reversed now, there would be a bit of an outcry.