Because that's what also included in the new proposed display entitled "Foundations of American Law and Government!

I like what Vonnegut had to say about our national anthem:
Trout and Hoover were citizens of the United States of America, a country which was called America for short. This was their national anthem, which was pure balderdash, like so much they were expected to take seriously:
O, say can you see by the dawn's early light
What so proudly we hailed at the twilight's last gleaming,
Whose broad stripes and bright stars, thru the perilous fight
O'er the ramparts we watched were so gallantly streaming?
And the rockets' red glare, the bombs bursting in air,
Gave proof through the night that our flag was still there.
O, say does that star-spangled banner yet wave
O'er the land of the free and the home of the brave?
There were one quadrillion nations in the Universe, but the nation Dwayne Hoover and Kilgore Trout belonged to was the only one with a national anthem which was gibberish sprinkled with question marks.
Breakfast of Champions
Really and truly, the only thing in their lame-o would-be display is the Constitution. If they really wanted a display of the principles of law and government we were founded on, they'd include the Magna Carta, the story of the Six Nations (Iroquois Confederacy), and the Emancipation Proclamation and leave the Ten Commandments and and our meaningless, war-loving, flag-worshipping national anthem the fuck out of it.