Not explained well, but similar to the anti-gay men who end-up getting busted on their knees blowing some dude in public restroom.  

In both cases, self hatred is the driving force.

I suspect a after a couple of minutes of weatherboarding and Cheney, Rumsfeld, and Yoo would be signing like canaries.  I think the mere mention of torture would have Yoo s****ing his pants.  They know that about themselves and hate it, so to prove they aren't any weaker, they torture others in hopes that they can broken, like they could be broken.

The LA Times details (about Ghul):

At first, his interrogators sought authorization to use "attention grasp, walling [slamming a detainee against a wall], facial hold, facial slap, wall standing, stress positions and sleep deprivation," according to the memo.

But the interrogators concluded that Ghul had steeled himself to resist physical pressure, the memo continues, so they switched to "more subtle interrogation measures designed to weaken [his] physical ability and mental desire to resist interrogation."

Those measures included "dietary manipulation, nudity, water dousing and abdominal slap." The team believed "those techniques would be especially helpful because he appeared to have a particular weakness for food and also seemed especially modest," the memo says.

A U.S. official who has been briefed on Ghul's role in providing Bin Laden information noted that "just because something was approved doesn't mean all of them were used," but he did not dispute that force was used.

"Ghul became relatively cooperative relatively quickly," the official said.

So.  1.  Still didn't provide any "ticking time bomb information."  2.  The most arguably terrifying techniques were not used because they were deemed ineffective.  3.  They relied mostly upon psychological manipulation, which appears to be the whole point of standard interrogation procedure.