BecauseKingRoot basically isn't able to work well on anything Nougat (7.0+) on up due to a whole complete change in system directories and the exploits were closed by the same guy who made towelRoot apps (he was hired by Google themselves, Lol). So, you'd need to use a PC to install CF_AutoRoot.zip &/or TWRP (for your SPECIFIC device) via ODIN.exe on Windows PC