Why does sub-zero hate scorpion?

Answer 1

they are brothers but subzero banesed scorpion from there clan and scorpion tried to get his revenge but he did in mortal combat

NO they are not brothers.scorpion killed sub zero's older brother aka noob saibot and scorpion thinks sub zero killed his clan

Answer 2

Sub Zero has never held any significant hatred towards Scorpion, it was always Scorpion who held a hatred. But Scorpions hatred was never directed to the Sub Zero that exists now, but in fact to his older brother, Noob Saibot. After Scorpion killed Noob, years laters he saw that the same Sub Zero was back, but he realized then that this was Noob's younger brother, and Scorpion had swore to not kill the Sub Zero that exists now(Noobs younger brother), but actually protect him.