Why didn't waterboarding work?

It seems increasingly clear that waterboarding was conducted to force a confession about ties between Al Qaeda and Iraq. After all the recent accounts on how effective waterboarding can be in getting people to say whatever the interrogator wants, why didn’t it work? Why didn’t the Bush administration succeed in getting Khalid Sheikh Mohammed to say he was involved with Al Qaeda, despite waterboarding him 183 times?

Perhaps they did get a confession yet knew it was inadmissible (or invalid) due to the circumstances under which it was elicited. But then why waterboard if the results couldn’t be announced proudly to the world: “IRAQI OFFICIAL ADMITS TIES TO AL QAEDA!”?

Perhaps the only explanation is that Bush officials honestly thought there were ties and that waterboarding worked. This is a defense but not a good one because it shows, in yet another way, how they were not listening to so many military and intelligence professionals who knew both.

What do you think?