Because fishing is boring enough to begin with and my dex 3 biologist keeps failing his attemps to catch fishes. And that is NOT FUN at all. The idea is cool but gameplay should be prioritized against flavor.
Or you could make the player be able to buy fishes to compensate but I guess nobody would waste time on fishing then.
Also, I just fished a sledgehammer next to the rathound king's lair, nice
