However, rather than activate his own lightsaber and strike down Rey, Kylo opted to activate Rey’s lightsaber instead and sliced his master in half.
After The Last Jedi’s release, director Rian Johnson revealed that he decided to kill Snoke to further Kylo’s development and make him the new Supreme Leader of the First Order.
With that kind of leadership change, Johnson didn’t think there was any point in keeping Snoke around.
It just goes to show that you should never insult your apprentice when a fancy laser sword is pointed in your direction.