Answer: Because he said so.
And that's good enough for us.
Lots of people have been asking that question about tomorrow night's speech by President Obama before a joint session of Congress.
First, here's what we know about a State of the Union address. The Constitution says that the president "shall from time to time give to the Congress information of the state of the Union, and recommend to their consideration such measures as he shall judge necessary and expedient." It doesn't say anything about giving it every year, or in the year of his inauguration. Nothing about the TV networks clearing their schedule.
Television coverage was not on the minds of either George Washington or John Adams when they delivered their message to Congress in person. Thomas Jefferson, disdainful of the pomp of such a speech, delivered his in writing. That's the way it was until 1913, when Woodrow Wilson gave his in person. The formal "State of the Union" address didn't become custom until 1947, with Harry Truman.
But why isn't Obama's speech tomorrow night a State of the Union address? A lot is about semantics. Even though he has been president for just over a month, if he wanted to call it a State of the Union he could, and that would be the end of it.
That's what President Eisenhower did, on Feb. 2, 1953. He wasn't especially wild about the idea of calling it a State of the Union address; after all, he was only in office for less than two weeks. But after 20 years of Democratic presidents, he wrote in his diary, it might be good for the party to give one ... to tell Americans there was a new sheriff in town.
Similarly, President Kennedy called his address to Congress 10 days after his inauguration an SOTU. Later, in May, he gave another State of the Union address to Congress -- a speech Kennedy decided was needed in the wake of the failure of the Bay of Pigs invasion in Cuba and the news a Soviet cosmonaut had orbited the Earth. (It was in that second SOTU where JFK called for the U.S. to land a man on the moon by the end of the decade.)
A State of the Union address is basically just that: a report on the state of the union. Both Ike and Kennedy wanted to celebrate their party's having taken over the White House, and they did it under the guise of a State of the Union speech. But sometimes a president wants his address to be far more focused. Obama wants tomorrow night's speech to concentrate on the nation's economic problems, not everything under the sun. And that's why it's not a State of the Union address.
That was the approach a newly elected President Carter took in April of 1977. He wanted his focus to be on energy policy, and that's what he spoke of. Likewise, on Feb. 18, 1981, President Reagan called his speech to a joint session of Congress a "program for economic recovery." He didn't want to dilute his message with anything else. He called for $54 billion in tax cuts and $41 billion in spending cuts, saying that America was in the worst economic mess since the Great Depression and warning of an economic calamity if his program were not adopted. (Sound familiar?)
Reagan gave another address to a joint session of Congress in April, following the attempt on his life. But it wasn't an SOTU.
Bill Clinton, elected on the "economy, stupid" platform in 1992, made sure his first address to Congress was about the economy ... and nothing else.
There is no rhyme or reason, let alone law, that says a president can or cannnot call an address to Congress an SOTU shortly after his inauguration. But no one has done it since Kennedy. And Obama will continue in that tradition Tuesday night.