Right...
Your starting to think... Now add this to the fact that the Juubi is a large mass of energy, which Obito was unable to fully control, and you arrive at to the main point which is why he was unable to just simple send select parts of himself to the Kamui dimension... Not to say he can't teleport himself there.
All you have to do read the viz scan... It's not that hard, then read up on how Kamui works because you lack knowledge of this, then read some more because you prolly still don't comprehend... Viola.