Why Kakashi did not kill TOBI

[garas56]

Kakashi doesn't want to kill Obito, for the last time.
Just like Naruto said he would protect Konoha without killing Sasuke, the same goes for Kakashi - he wants to protect Naruto but not kill Obito.

This also may be truth(he want change obito not kill him)

[KGB Kakuzu]

I mean we don't know how much chakra Kurama fished out...he might have waited to make sure he had enough to Kamui. Also it could be that if Tobi dies the demension is closed or there is a problem with it (could argue that Kakashi's eye has the same demension).