My guess: Bush just doesn't care anymore. He's proposed his solution via Paulson but he'll sign anything because he's written his legacy off. He doesn't want to lead on this because he's checked out and already feels repudiated. As well he should--he's been a lousy president, and that's more than likely how he'll go down in history. And his unwillingness to go on TV and, you know, tell us what's going on confirms his deficiencies as a leader.
Update: Bush is going to be on television tonight to talk about why Congress should pass his plan. Hmm...timely.
Update 2: Clay Risen says what I said, and brings up Lyndon Johnson, another hated President during a crisis:
Within minutes of Martin Luther King, Jr.'s assassination on April 4, 1968, President Lyndon Johnson had his aides cancel a trip to Hawaii and book airtime on the networks. Within 24 hours he had gone on television twice, met with Congressional and civil rights leaders, and made a high-profile appearance at the National Cathedral. And this was a man so unpopular that he had pulled out of the presidential race just four days earlier (his poll numbers had since shot up, but he was still a lame-duck president). Johnson's appearances didn't prevent the ensuing riots, but as a demonstration of grief and concern from the nation's political establishment, they likely had a dampening effect on further outbursts of violence.