The MOAB delivered the equivalent of 21,000 lbs of TNT. A big blast, yes.
But during WWII the B24 carried 8,000 lbs, and they dropped hundreds of loads on Germany. In total the British and Americans dropped 136,000,000 lbs, the equivalent of 6476 MOABs.
And we still had to put something like a million boots on the ground.
No ISIL isn't the German Army, but they are spread out over lots of territory. Maybe we killed a few dozen, or even a few hundred with one MOAB. Impressive, yes, but still a drop in the bucket.
As far as I, personally, am concerned, we shouldn't wast our time, money and men.
Let the Saudis, Paks, Afghans, Kuwaitis, Turks, Syrians, Israelis, and all the other mideasterners fight them.
We've flushed too many Americans down shitholes before...Korea and Viet Nam and Iraq.