I’ve speculated as well that it might be part of a grander strategy. Basically Al Qaida means “the base” and the original “base” was a training camp in the Frontiers of Pakistan. Now they are forced into fighting on their home turf, and… their jihadi chickens have come home to roost.
Their strategy changed to defense and taking over the frontiers in Pakistan in 2006 when they saw the surge coming in Iraq.

This has certainly allowed us to win in Iraq, and it’s taken a great deal of pressure off the lightly manned Afghanistan. Hell on the Pakistanis, but an effective strategy for us.