"Mr. Leno dominated the late-night ratings since the mid-1990s, rarely losing even a night to Mr. Letterman. But NBC faced a dilemma in 2004 when Mr. O?Brien, at the time one of the hottest stars in television, had offers to jump to a different network. To prevent that ? because Mr. Zucker and others concluded Mr. O?Brien represented NBC?s future in late night ? Mr. O?Brien was offered ?The Tonight Show? after a five-year wait."
http://www.nytimes.com/2010/01/15/bu...a/15conan.html
like I said it was all corporate.