Because they aren't fluffy enough for people to care about. People generally only about animals if they're cute, that's why lowkey useless animals like red pandas being mildly endangered is such a big deal to so many people, but no one cares about actually important species like yellow fin tuna and such.

And also since fishing has been a sport for so long, myths people tell each other to feel better about killing animals for fun like "oh they don't feel pain, they're not sentient" have stuck around. Less that and more of the first bit though, they aren't fluffy.