Could it be a case of habituation?
That is probably the reason they don't fish well or at least a part of it. If they were fished to the same degree as maggots and castors it might be different story. I would have thought these were easier to produce on a commercial scale. You don't have the problem of them turning into flies and having to start all over again and you can feed them on bran and bits of potato. I would have thought this is cheaper than meat albeit cheap meat which maggots have to be fed on. If they were available and used on the same commercial scale as maggots the fish would soon accept them as food I would have thought.
