Hands compare to faces have a lot of limbs, they can take many different poses that makes it difficult for the model to learn them, also these models are usuall

Hands compare to faces have a lot of limbs, they can take many different poses that makes it difficult for the model to learn them, also these models are usually not good with "counting", an hand has 5 fingers but you can easily expect that a model will create an hand with 4, 6, 7 fingers.