I don't think Bush really wanted to win.
My dad always says that but still...that big of a loss?
His heart just wasn't in it. I think he was repulsed by the ugliness of Washington, and he really had little idea about why he wanted to be president. Unlike Clinton, his ego wasn't big enough to want to be president just for the sake of being president.
He ran out of ideas and steam. Bush did some very good things as president, responding to the Iraqi invasion of Kuwait and managing the collapse of communism in Eastern Europe. But after that, he had nothing left. I voted for him in '92 without much enthusiasm because I didn't think Clinton and his wife were trustworthy, and I just couldn't bring myself to trust the Democratic party on critical issues like national security.
But when the base has no enthusiasm for the candidate, he is done. I'm sure Bush didn't want to lose on a conscious level, and he clearly wasn't willing to walk away from the office, but he also wasn't willing to do much to avoid losing.
Bush pere really ticked off two key constiuencies. Those who do not like tax increases and his support for gun control.