TV’s Frink said:
And how do you know Luke told anyone what really happened anyway? He could have easily wanted to keep the whole thing to himself.That’s been suggested somewhere before, but in my mind, it’s absurd. To understand why it’s absurd is a bit complex, and many people won’t take the time to digest it, but it is absurd.
Here’s why: Vader’s redemption is probably the happiest, greatest thing that has ever happened to Luke and a shining example of how GOOD TRIUMPHS OVER EVIL.
With Yoda’s passing, Luke is now the only champion of the Jedi Knights. He’s the only one. It is his duty, his calling, to tell a whole new generation about the Light Side of the Force and warn them away from the terrible dangers of the Dark Side.
So as the new Head Chief Jedi, Luke’s job, Luke’s duty, would be to spread the message of the power of the Light over the Dark. As Yoda said, the Dark is not more powerful, but it’s easier and seductive and must be resisted.
There simply would be no better story, no better evidence, no better shining example of how GOOD TRIUMPHS OVER EVIL than the story of Luke’s very own father.
That is not something he’d just keep to himself.
And like I said before it’s more likely that he would tell his close friends and his students at the academy then telling the entire galaxy. Also seeing as how the Galaxy can’t decide who Han Solo is there’s no saying as to whether the entirety of the galaxy in it’s totality would accept Luke’s news.
EDIT:
Also maybe Kylo Ren is in denial over Vader turning to good. I remember bringing that up too.