My gut on this, which is as unreliable as any gut feeling goes, is that Obama felt that as the first black president, he would be wisest to play mainstream, no drama, steady as-she-goes. I think he, and his close supporters, knew this was a watershed event, and they wanted to ensure they could say "see, a black man as president, and it's not the end of the world."
Of course, never underestimate the racist south, conservatives, etc., who demonized Obama from day-one for nonsense like the birther, being a Muslim, etc., and ended up voting in Trump on a racist, xenophobic, nationalist platform. Surely a backlash from having a black man as president...
But did Obama play it safe? Most likely so. And historically, it seems like a wise move, if not an understandable one.