The short and easy answer is because the state legislature voted it that way. The more complex answer is that there are a lot of nonsensical laws on the books which make no sense today. Fish roping would appear to be one of those laws.
I'm not sure. It could be because lassoing a fish is considered cruel. Lassoing a fish is inhuman and can be painful for the fish. Lassoing a fish would be like torchering a fish.
