I dont think it's so much an overall dexterity issue just a practice issue. Someone who doesn't regularly use chopsticks might have really high hand dexterity but they just haven't practiced that finger coordination. I.e. its easier to teach an athlete a new sport but a football players gonna have to practice to play hockey well.
The most common mistake I see with infrequent chopstick users is overgripping and a low grip. If you squeeze too hard it not only fatigues your hand but it actually makes them harder to control, same for choking up on them. If feels more secure but it actually gives you worse control. For any one wondering a high grip and only as tight as you'd hold a pen should make it easier to use chopsticks.