Problem is, if the drop the case, there’s no ruling in favor of those arrested.
Which means the police chief doesn’t have to stop doing what he’s currently doing. He will keep arresting people.
This is what the West Allis police chief is doing, despite a court case saying so. The reason was the judge said “in this particular case there was no disorderly counduct”. Chief doesn’t change his procedures because the next case may be disorderly so cops’ actions to arrest while open carrying may be justified.
That's the beauty of the civil rights lawsuit. The tyrants can't "drop" it unilaterally. They may be able settle, but only on terms agreeable to those on the other side (revised policiing procedures acceptable to the arrestees, etc.).