Board Thread:Episode Discussions/@comment-1181222-20171213112025/@comment-33953813-20171215062938

Ninjustsu is something which ninja have an affinity since childhood. It's not something which can be incorporated in someone only because they wish to do so. They need to have a natural affinity towards it.

Ninjustsu requires a specialized set of skills which everybody doesn't have.

Besides I think they made Rock lee a jonin considering his sheer strength in taijutsu can take several enemies even with advanced ninjustsu abilities.