Why would someone continue to fight in a battle after the war was basically over

It really depends.

Explanation:

There are many reasons someone would fight after a war was over. Even after world war one, many fought for a monarchist Germany, due to their national pride. Or maybe it was because they believed in a government that was different to the one they were assigned after they lost a war. After WW2, many soviets continued to fight Germans and kill them, due to their part in the war, and how many lives the Germans had claimed. It really depends on what happened during the war, what the outcome was, and more.