its simple.. obito's MS has two abilities.
kakashi's left eye- The left eye's primary use of Kamui is based on line of sight and, as such, does not require physical contact to warp a target into the other dimension (also, Kakashi doesn't centre Kamui around his eye unlike Obito). By focusing to create a barrier space and concentrating on the target within, Kamui will distort space and the target will be drawn into the other dimension. When Kakashi first used this technique, it required great concentration and was difficult to aim, dragging in only Deidara's arm when he aimed for his head. During the Invasion of Pain, Kakashi was able to use Kamui to stop a speeding nail from penetrating his head. Later, during the Fourth Shinobi World War, Kakashi also displayed the ability to teleport himself.
obito's right eye- The unique trait of this eye is the ability of intangibility. When activated, any part of Obito's body that overlaps with a solid object is seamlessly warped to the other dimension, making it appear as though he is phasing through them. Using this ability, Obito can dodge most attacks, and by overlapping his entire body into large objects, he can not only conceal himself from view, but erase all traces of his chakra. Obito is also able to travel through the ground using this ability; a characteristic he often exploits to ambush his opponents from below. Though he is unable to establish any physical contact while being intangible, Obito can still use chakra chains. He also seemingly possesses the capability to extend this intangibility to whatever he's touching at the moment of activation, as long as he is able to maintain some form of contact with at least a part of the desired item or person. Obito centres his Kamui around his right eye and also requires physical contact with the target to warp them.
when obito was the juubi jin, he couldnt kamui himself because of his right eye ability (overlap himself). Likewise, in kakashi's case his left eye doesnt have the same ability as obito's right eye, meaning kakashi cannot overlap himself. He can just move objects to the other dimension. Now, when madara eye-jacked kakashi's sharingan he just teleported himself to other dimension.
question..?
