It is widely stated that the reason behind Luke Skywalker’s self-imposed exile during Star Wars: The Force Awakens was that he considered himself to be responsible for the events at his Jedi Academy. He was training a new set of Jedi, one of whom went to the evil Dark Side. His own nephew caused the killing of the other Jedi barring Luke. This leads us to the question – why did he run? He has earlier battle the Empire, on his own so why would he run away from the Republic, ditching his sister, friends, just because one of his students joined a Dark Side lord?
We have no clue about the identity of Snoke. Vader went easy on Luke because he never fully believed in the Dark Side. Sidious just toyed with Luke. Therefore, Luke has not really battled (in the new canon that is) a real Dark Lord at his extreme powers. Snoke might not be Sith, but Luke is not a proper Jedi. He just got some kind of training and the rest he has just learned on his own.
Therefore, the truth could be that Luke is genuinely challenged by Snoke and he ran away only to gain more knowledge that enhanced his power. The extermination of the Jedi meant that he had no teacher to add to the knowledge that he learned from the two before they died. The only ideal place seems to be the ancient Jedi Temple, away from the Empire. It was brilliant on Lucas part to surmise that the legendary and fast lightsaber duels were the result of inadequate learning after the Jedi purge and the fall of the surviving masters. Luke only received a very basic training in the Force and Lightsaber topics. The truth is that the padawans of the Clone War days knew Force better than Luke.
The Jedi were arrogant, and they considered themselves to be almighty and so much in command of the galaxy that they didn’t consider a purge a possibility. They were indeed at the top of their powers. Sith were manipulated by the Rule of Two. Therefore, their training was considerably safe.
The Rule of Two is a Sith custom implying that only two Sith could exist at one time. One would wield power and the other desire it. This ensured that the internal fighting was least and it only ran on the premise of each Sith being more powerful than his predecessor.
We don’t believe that Snoke is a Sith, but, apparently, Dark Side has many ways to safeguard their teachings. There was no purge of their texts because they were generally assumed to be non-existent.
Luke was better off escaping the battle and learning. Yoda was gone and so was Obi-Wan, however, their spirits were there to guide him. They might have told him to visit an abandoned world to learn more about how to defeat the enemy. Jedi didn’t believe in launching a full-scale attack to beat the enemy. Therefore, the wise thing was to beat them with knowledge and understanding instead of sheer force.