It isn't about hitting them, but controlling the space around the ball. If the mines don't move, we know there aren't any klings cloaking without five feet of us waiting to tractor/VM us for a focus fire hell.
No klink ever intentionally flies into a mine field. But once the fighting starts and the beams have whittled away shields on both sides and people start maneuvering around, they do tend to get within 2-3km of minefields. I routinely get kills from my blue quantum mines as fed. Even against premades that wipe the floor with a fed pug, inevitably a few will stray too close to a mine field with their shields down.