Although the Bush administration hunted Osama bin Laden for seven years with the intent of capturing or killing him, they failed. It then took the Obama administration just over two years to do what the Bush administration failed to do.
The Bush administration did not find Osama bin Laden simply because they weren't trying too hard. If they wanted to, they could have, but shortly after September 11th, the Bush administration wisely turned its focus to the conflict in Iraq for the ultimately successful hunt for WMDs. Due to the Bush administration's efforts, Saddam Hussein was deposed and could not use his stockpile of WMDs against Israel or the US, and the Taliban and Al Qaeda were driven from Iraq. OBL was small potatoes compared to this important goal. The 2011 assassination of OBL was a symbolic victory for the Obama administration, nothing more.
The record is clear from Bush's statements about OBL.
First, on September 13th, 2001 -- just two days after the attack:
"The most important thing is for us to find Osama bin Laden. It is our number one priority and we will not rest until we find him."
Just a few days later, on September 17th, 2001:
I want justice. There's an old poster out west, as I recall, that said 'Wanted, Dead or Alive.'"
As the Bush administration focused on Iraq, the hunt for OBL was de-emphasized. Bush made this clear on December 28th, 2001:
"...Secondly, he is not escaping us. This is a guy, who, three months ago, was in control of a county [sic]. Now he's maybe in control of a cave. He's on the run. Listen, a while ago I said to the American people, our objective is more than bin Laden. But one of the things for certain is we're going to get him running and keep him running, and bring him to justice. And that's what's happening. He's on the run, if he's running at all. So we don't know whether he's in cave with the door shut, or a cave with the door open -- we just don't know...."
By March 13th, 2002, the Bush administration had moved on:
"I don't know where bin Laden is. I have no idea and really don't care. It's not that important. It's not our priority.... I'll repeat what I said. I truly am not that concerned about him."