Great, we have 8 people who support letting ISIS get away! As long as the dear leader Trump says to do it, Trump followers will do it.
Where is Syria in all this? Have they stopped fighting? Why can't they take over?
They could take over.
Syrian Civil War Map - Live Middle East Map of the Syrian Civil War
(the ISIS pocket is in the extreme southeasterly part of Syria - in dark gray)
The only part of Syria that still has an ISIS pocket is in the Kurdish-held region (a region they stole from Syria when Assad's forces were getting beaten in the Civil war).
This region is where US troops are. And Syria does not dare attack this region so long as those US troops are there.
Now that they (might) be gone - Syrian government troops could now eradicate the last ISIS pocket of resistance.
Especially since the Kurds seem unable (or unwilling) to close the pocket themselves.