Violence in Iraq has remained pretty steady since December 2017, and ISIS has been responsible for the majority of it, even accounting for and removing the death tallies due to the mass graves that the Iraqi Army keeps uncovering.
And it's not like this wasn't predictable. What did they do in 2008-9? Retreat to the remote areas of Ninewa and Diyala governorates, establish zones of control and income (protection rackets, kidnapping, smuggling and hijacking). Use those to fund attacks on outposts and assassinations of local political, military and religious figures. Put in place a shadow government, build up forces until sufficient manpower allows for the overthrow of the state. It's classic guerilla warfare, Mao style. They dominate the countryside, then infiltrate the cities, then establish parallel control.
The Iraqi security services all know this, of course. The PMF commanders in particular are under no illusions - they know they're marked for death by ISIS assassins. But try getting anyone in any actual newspaper in Europe or North America to take notice. Nope, "mission accomplished" time to pack up shit and pay attention to something else. Again, just like 2008-9, when most foreign correspondents pulled out of Iraq. And then they were surprised when ISIS took Fallujah and Mosul, claiming "no-one" could have predicted it, when *ahem* some of us did.
