Because it will be fun watching Rhodey's head explode.
Because that mixture of surprise and anger is a good look on Pepper.
Because nothing says "Tony's gone round the bend" like implying that he needs an armoured bodyguard.
Because no one would believe that ridiculous bodyguard story anyway.
Because it's less trouble than dodging the media until some photographer gets a picture of Tony Stark in the Iron Man armour.
Because that fifty-six point loss in the stock market? Finding out that the head of the company is an honest-to-god superhero should take care of that by the close of business tomorrow.
Because the board is going to love having that shiny new technology, no matter what he's using it for.
Because a public announcement is one hell of a way to keep someone else from claiming they invented the damn suit.
Because he's been wearing one mask or another—boy genius, hedonist, merchant of death—all his life and it feels good to admit something about himself that's true.
Because Obadiah would have hated it.