Did he give the speech in blackface? He's not really black, you know. He's a mullato. His white mother and grandmother raised him to act white, so that he would be accepted by their white liberal friends.
He used the "I'm not an angry negro" facade to trick liberal white people into voting for him in 2008.
He defied the stereotype. He posed as a "respectable negro" who wasn't angry or scary. A "credit to his race" as my blue-haired old liberal college professor aunt called him.
And he spoke in proper English, not "Ebonics". College educated liberals could understand him. Joe Biden even praised him as "articulate and bright and clean and a nice-looking guy".
He was the perfect candidate.
He didn't pick up this "home boy" schtick until it became convenient for him.