There's a difference between the two Kamui's. If Obito wants something in a different dimension back to the original, he has to bring it out himself, while Kakashi can only send material to it.
Kakashi would only kamui its head, not the whole body, as it was stated many chapters back. That would kill the Juubi, and Obito bringing its head back wouldn't serve to revive it.
Besides even if Kakashi could just Kamui Juubi head, Juubi could regenerate it(nature chakra) or simply make it come back and somehow attached back to rest of this body.
Common, Juubi is origin of sharingan powers. Kamui, Amaterasu, Tsyukomi, Kotoamatsukomi, Sussano are Juubi abilities and easy to counter for Progenitor of Shinobi World=D