remember when lee wanted to take his medicine? he just stood there and observedHe needs blood, and time to do his ritual, he's hard pressed to get any blood from Kimimaru to begin with, but do you think Kimimaru would give him time to draw a circle of blood with the triangle in it for his ritual?
It was easy with Kakuzu backing him, but solo he'd never get the chance, nevermind the fact that kimimaru is a blade specialist and can use projectiles, all this means that Hidans limbs will be all over the battlefield, not to mention he had access to curse mark