Quote Originally Posted by Zero View Post
Most likely because they are not So6p or an Uzumaki (?), who can seal it in himself without anyone's help. They probably need help in sealing it (it's a creature with an infinite amount of power after all), or at least someone needs to keep it in control, so that it won't go berserk in the middle of the sealing process (this means that they are unable to become it's jinchuriki, without the other's cooperation).
But doesn't that create another problem, what's to stop the Jyuubi from overpowering the Jincuuriki and busting loose when they try to tap into it's power.

It's all going to end badly either way.