Why cant kakashi use kamui like uchia madara does?
Kakashi isn’t an original Sharingan user. It’s not something he inherited or was born with. It’s something that Uchiha Obito gave him right before he died. A good point in noticing the difference is Madara, Sasuke, and Itachi never had to really prepare their sharingan, they could quickly switch eyes. Kakashi has to prepare his sharingan in most cases (like when he tries to use Mangekyo Sharingan). He’s never known as a sharingan user, rather the “copy cat” user who mainly uses it as a defensive strategy and it’s ability to read chakra to predict movements and hand signs to use the same ability as the enemy. Because of this though, his body, or rather chakra, isn’t suited towards prolonged use of the Sharingan, hence why he can’t use an ability repeatedly. Edit- I should also mention that each Sharingan user unlocks an eye jutsu special to them. For instance Itachi had Tsukiyomi and the Amaterasu, which sasuke only obtained after Itachi had implanted the ability in him before his death
