I read recent thoughtful reports speculating one purpose, maybe THE purpose, of the attacks on Paris were intended to induce Europe to close its borders thus stopping, or at least slowing, the out migration of the Syrians from ISIS controlled or influenced areas. The Syrian population in the IS controlled areas have been maintaining at least the semblance of an economy as well as serving as hostages against stronger conventional warfare tactics. If too many Syrians leave it would not only destroy any local economy, it might make the IS itself more vulnerable to conventional military action.
If ISIS is looking to keep the local economy going, not killing the Syrians who are living in the towns might be a good place to start.
