And for vegetables: Forks are pointy, you can just stick it in there and eat.
Forks would have a rough time with kinpira or bean sprouts:
Sure, you can treat them like noodles and just fork a whole glob of the veggies, but the point is chopsticks gives you precision. You can get half the bowl or a mouthful, or even a single strand, according to your will.
With a random spread of Chinese/Japanese/Korean food you don't know if you need forks or spoons or both, and it's more efficient just to use chopsticks because it's the most generalist utensil for East Asian cuisine. You can even use chopsticks for molluscs and crustaceans like clams or crab, whereas you'd have to resort to those tiny forks as normal sized ones are too clumsy. Rather than have 3 different kinds of forks and spoons, we just have chopsticks and the porcelain spoon. Forks would also shred the meat on a lot of smaller fishes like Mackerel or Saury, stuff you sometimes eat off the bone which makes both spoons and forks awkward to use.