ISIS previously controlled a LOT more of the now green north (go look up some older maps!!!) & have basically been pushed back into their present enclaves, mainly by the Kurds. The ISIS enclaves are areas they TOOK from the Kurds, and may now be contained by the Kurds, but are certainly not yet “controlled” by the Kurds. To suggest that, or that the Kurds / US are somehow deliberately shielding ISIS from Assad is disingenuous at best.
I would add that I get the impression progress against ISIS has slowed due to the Kurds having to worry about Turkey.
I’d also add that that map is a bit misleading: Inside the blue area and even in the green area are smaller areas that really no one controls. In some desolate places, perhaps no one cares a lot @ present.
The US has and will attack any pro-Assad forces that cross the Euphrates from the West, an action that is required for pro-Assad forces to reach the ISIS camps on the Iraqi border.
Meanwhile, nothing is being done to eradicate those camps by the Kurds or the US. Its obvious that ISIS has been given a safe haven in the Kurdish zone, just like the one they enjoy in the Golan on the Israeli border.