to attempt to make sense of a plot character. Kishi realized he was making so much ass-pull with obito that he had to show his MS at least once, even though it's completely pointless since he already has the full capabilities of Kamui.
Anyway, if you want logic -> His MS has been shown to spit things out of Kamui dimension only. Maybe his Kamui releases things from kamui dimension, and kakashi's own Pulls things in. Maybe obito's using remote kamui through kakashi's eyes. Maybe this is all BS and theirs no explanation for retcon.