Islamic State uses improvised weapons of war in Mosul, Iraq | FDD's Long War Journal

It is a part of insurgent strategy that no one never addresses; cost to kill. They hide among civilian populations. We fire a missile that costs tens of thousands or hundreds of thousands of dollars to get a dozen "surgically precise" casualties. They use $20 worth of crap from a hardware store and don't worry who it kills.

They will continue to use/expand this tactic. It's working, it's demoralizing, and it's cheap. Don't expect it to go away anytime soon.