M-1 tanks require lots of maintenance. They’ll be abandoned on the roadside by the Isis crews when they break down.
The turbine engines that power the Abrams are supposed to last 700-1400 hours TBO, which apparently means replacement.
We’re not just giving Iraqis and “moderate rebels” in Syria weapons, we’re training them. The US has probably trained a lot of ISIS soldiers, and continues to do so.
They’ll be used as artillery pieces. The hand controls never break. So they have the capability of dragging them within range of the next town, and terrorizing them with the main gun. I think the real limiting factor is ammunition.