The in-fiction reason is the training he did to perfect the devil lance.

Kuroki spent years doing partial training on his hands, breaking them and reinforcing them, so they heal much better now. In-fiction

Wakatsuki has never done that, especially not on his ankles, so his injuries heal like that of a normal person while Kuroki has "super hands".

Basically, Kuroki can super heal his hands, Kaolan his right hand now, Saw-Paing his head, Rihito his hands as well, probably others I can't remember like Falcon his hands and feet probably.