Picking from several recent pieces Gareth Porter adds one and one together and finds the rather stupid reason why, after mid 2008, the CIA increased its drone campaign in AfPak.

Despite that disastrous start [in the early years of the drone campaign], however, the CIA had quickly become deeply committed internally to building a major program around the drone war. In 2005, the agency had created a career track in targeting for the drone program for analysts in the intelligence directorate, the Post article revealed.

As there was now an internal carreer commitment by the CIA to its personal in the drone business, that business had to be increased. This even after it had turned out that drones attacks are an ineffective tool with negative strategic effects.

By 2007, the agency realised that, in order to keep those commitments, it had to get the White House to change the rules by relaxing existing restrictions on drone strikes.

That's when Hayden began lobbying President George W. Bush to dispense with the constraints limiting the targeting for drone attacks,[…]
…
Released from the original constraints on the drone programme, the CIA immediately increased the level of drone strikes in the second half of 2008 to between four and five per month on average.

And it grew and grew from thereon.

Similar internal mechanisms are active within the military. All those additional special operations forces hired and trained after 9/11 have soldiers and officers on career pathes they want to continue. Instead of winding down after Bin Laden has been caught they will be actively looking for new targets.

This is a "supply side economics" run wild. Having committed to sustained supply capacity, as the CIA did with the drone analyst career offer, sustained demand, new enemies, new terrorists, need to be created. For those secretive people working the dark and dirty side of the war business that is not a problem but part of their specialty.

The "war of terror" is now engraved into the organizational structure of the CIA and the special forces. It will therefore only end when the U.S. will lack the money to continue it.