Because Kamui isn't as good as Kakashi and Minato fanboys say it is.
I guess a hand throw kunai is faster than kamui.
Because he wouldn't be able to bring guy back (though would have saved him). And when it comes to kamui'ing humans, unless it is prepped or charged it isn't instant.
just last chapter kishi spent 4 pages showing single kamui teleportation isnt fast enough against black orbs
you guys have piss poor memory