ISIL have a lot of pilots, with varying levels of experience - that isn't the problem for them. Their problem is maintenance and spares, as well as airframes, since the only kit they get is what they can scavenge or steal.
A few months ago, they released photos of captured planes and they were all (at least the ones in the photos) wrecks that had been stripped for parts or mothballed badly by the Iraqi Air Force. Doubt a single one of them was capable of starting, never mind flying, without several thousand man hours of work. Not the sort of work your average alleyway mechanic can deal with either.
Add in their problems with basing - choppers can work from almost anywhere, jets can't - and their concession of the skies and emphasis on MANPADS in their arms mix makes a lot of sense. I fully expect a few cheese targets to be offered, if they haven't already: an apparent high value force accumulation to sucker in the fighters to manpad range.
