Why is Hua Cheng's handwriting so bad?

Does anyone know why Hua Cheng's handwriting is so bad? Maybe I'm just overthinking it and he's just bad at writing, but he's pretty talented in general.

My theory is that he might be left handed, but I don't think the novel explicitly said so, or I missed it.

Has anyone else wondered about this or am I just thinking too hard about it?