Why did America just drop the mother of all bombs?
There is the glib answer: Because we can. Then there is the technical answer: Because it was right for the job.
The U.S. military on Thursday dropped its largest non-nuclear bomb, the GBU-43/B Massive Ordnance Air Blast Bomb, on an Islamic State, also known as ISIS, target in eastern Afghanistan. The bomb, which weighs 21,600 pounds and extends 30 feet long, had never before been used in combat.
In military operations, one of the considerations is to be proportional—use coercive force commensurate with the task, while taking due diligence to protect innocents.