There are objectives that are desirable and obtainable.
The current objective is to draw boundaries between ISIL and the Kurds in the north of Iraq and the Shia in the south. The bombing has been worth while in that very limited objective.
Iraq is partitioned. There is no more Iraq in the old sense.
Ditto Syria but the boundaries are more tenuous. I expect ISIL will turn on Aleppo again when the status in former Iraq becomes more stable.
Then no wonder Iraq won't fight. They have nothing to fight for. Who will supply the ground troops - endless dead Americans and endless billion bucks?