I believe the past few chapters should have revealed to you that Kakashi can only use Kamui that much with a few chakra boosts from Kurama.
That said, Itachi isn't going to stand in one place and wait for Kamui to happen.
kakashi can beat itachi as itachi can't counter kamui
itachi can't beat kakashi as kakashi can counter susano,amatrasu,tuskiymiu
kakashi used 6 kamui and 5 raiki,light chain,shadow clone,earth wall so with full chakara and without using other justu (remember one of 6 kamui was on the gedo's head)
kakashi can use kamui with full chakar at least 10 times on objects as big as human
kakashi can kamui 1/3 hatchibi twice >>>>suasno
kakashi can go in and out from the other dimensiom
itachi can't escape from kamui (it is fastest attack)
kakashi warped naruto(fastest ninja move on his feet) without obito who has sharingan note
kakashi warped susano arrow (one of the fastest objects)
you speak about kakashi's kamui as it take a century but it take apart of second
you speak about kakashi's kamui as it move but it appear with just a look ,it is instant jutsu
you speak about kakashi's kamui as it need to connected eyes but it doesn't
you speak about the tuskiyumi as it is kamiu (doesn't need to connected eyes)
but the tuskiymui need connected eyes
you ask why itachi will let kakashi to warp him (i answered that)although the right question is why kakashi will look at itachi's eyes
whatever, kakashi can counter it with his ms