Why the 'Mother of All Bombs' and Why Now?

Article/Op-Ed in CNN
April 14, 2017

Peter Bergen wrote for CNN about the Mother of All Bombs: 

The dropping of a "mother of all bombs" Thursday by the United States on an ISIS cave and bunker complex in Achin district in eastern Afghanistan should be understood as part of an effort to reverse a war that is not going well for the Afghan government and, by extension, the United States.
The non-nuclear 21,600-pound GBU-43/B Massive Ordnance Air Blast Bomb (MOAB) "targeted a system of tunnels and caves that ISIS fighters use to move around freely," White House press secretary Sean Spicer said.
Thursday's bombing had a feeling of deja vu. A decade and a half ago the US Air Force dropped massive 15,000 pound "Daisy Cutter" bombs on the Tora Bora complex where Osama bin Laden was hiding in December 2001. Achin district is only a dozen or so miles from the Tora Bora region.