Why can't we find bin Laden

The WaPo informs us that not only haven't we found Osama bin Laden, but that his trail has gone completely cold, at least for the Pakistanis, on whose territory he's widely presumed to be hanging out.

The key graf in this article, however, is Musharraf's account for why the Pakistanis have been unable to find bin Laden:

The United States shares major responsibility, Musharraf suggested, because the U.S.-led coalition does not have enough troops in Afghanistan, which has left "voids." The United States and its allies need to expedite the training and expansion of the new Afghan army as the only viable alternative, he said.

Anyone care to venture a guess as to why we don't have enough troops in Afghanistan, hunting down the man who actually attacked us on 9-11?