I notice that not that many people train their forearms directly, my question is why?

Is it because you believe that forearm work is not needed, because the muscle fibers get enough stimulation while doing deads and curls? Or do you just choose not to train forearms?

For me, my forearms are disproportionate to my upper arms, they aren't any bigger than the average persons lower arm. I always hear people say that you need to train your legs because they make up half your body, but dont forearms make up half your arm? Im sure no one on here neglects their triceps, so why do so few people do direct forearm work?

I cant see how they are worked enough through other exercises either. You cant tell me that if I were to do 0 forearm work, they would be the same size after 4 months or so of training, as if I did train them directly?

Or am I wrong, is forearm work really useless? If I wanted to really add some mass to my lower arms, what exercises should I do, and how many sets?