The Iraqi forces have found out that the US aircraft usually airdrop arms and food cargoes for ISIL militants who collect them on the ground , more info here : https://www.youtube.com/watch?v=us1zugbskrs
How do you think that the ISIS was able to procure more than 2,300 American Humvees? Don't be naive enough to think that the Iraqi soldiers left behind all of them in the battle. From the beginning itself, the Americans and Israelis have blocked every single plan to send weapons and aid to the Kurds, who are the most effective fighting force against the ISIS as of now. And at the same time, they seems to be having no issues in sending supplies to the ISIS barbarians.