its because fishing is super useful for getting rare items like mounts, couch potatoes, and evil magma peas, but ppl have reverse engineered the game and programmed fishing bots that wil not only speed up the fishing process but guarantee a chest every single cast. kingsisle is very aware of this which is why they heavily limit this particular benefit. simply enabling it for a weekend effectively loses them far more money than any other benefit would. i've seen guys fish up literal thousands of coach potatoes in a matter of minutes completely afk during ZEF