There is a strange misconception in the U.S. government that the war in Ukraine is about the territory of Donbas. They believe it because... putin said so? They just cant stop repeating nonsense about giving up Donbas, right?
It is not a war for Donbas. It is a war to destroy Ukraine as a state, strip away its independence, erase Ukrainian culture, expand the russian empire, and carve Putin’s name into history as a new emperor, or something close.
In this context, giving up the most fortified territory of Ukraine - the remaining part of Donetsk region - without a fight would be the stupidest move. It simply cannot happen. Because once Russia takes the most fortified territory of Ukraine without resistance, it gains better ground to attack further, to reach its goal, and to destroy Ukraine. And it absolutely, undoubtedly will do just that.