Like swimbait said hooksets is one reason,also there might be something in the water you are not aware of.After a fish is hooked at times they will ram there mouth where the hook is into rocks under water to break free.They do not have much for teeth but as you know they shake there head a lot if the hook is deep in there mouth and the line is over there lips,shaking of the head on your line there sandpaper lips will cut 6lb test.I dont think you will be missing bites w/ heavy line.They will also use the sides of there gill plate by running away from you and shaking there head to fray the line.I dont use anything under 17lb test I use up to 30lb test in cover,6lb test is just to light.