He probably disappeared because the DNC was still propping up Hillary Clinton and she was running the show. Remember 2008 was supposed to be Hillary’s year, Obama came out of nowhere during the primaries, he was just a one term senator. So the DNC and Hillary probably felt that Obama swiped the presidential seat from under their nose. Obama gave Hillary Secretary of State as a peace offering, but probably wasn’t enough for the DNC and Hillary. I doubt he could have pushed through any meaningfully change when the DNC was adamant on getting Hillary in office.