I have no idea. There are far cleverer people than me advising the politicians on their possible course of action.
Why these clever individuals resort to a tactic that plainly doesn't work is beyond me.
I fear it is possible that the advice is "Well you'll have to do something violent otherwise...
It feels like both sides have got what they wanted. This was always the inevitable consequence of their actions.
ISIL have been goading the US with horrific acts, to provoke the desired reaction.
The US, as ever, feel they have to kill many more people in a technologically superior and "clean"...