They have a playable nearly finished product with the source code. That can cause a lot of damage if mishandled.
Personally I am 95% positive the leaker has not played the game and is pretending to have, to increase his clout.
My reasoning being
1) he released to show a single piece of evidence or even talk about the game. A random ass screenshot of Let’s Go was leaked before reveal and no one cared. If you kept it low profile enough, you would not attract attention or trouble.
2) Was scared to say **** but then decided to start talking about how the shiny noise and effect is back and how Stunfisk is in the game. Two things that would not be provable until release and if you were so scared why speak at all when the headlines are going to be “LEGEnDS ZA HACKER REVEALS UNRELEASED INFORMATION ABOUT THE GAME!”
3) the people from his discord claiming he shared were all trolling and said they don’t even have any evidence it actually exists from the leaker.
4) not a single piece of information or pictures leaked. All leakers are clout chasers and there’s no way something wouldn’t have leaked by now. So many easy ways to do it and not get caught, yet they chose not. But they can comment on a random returning pokemon and not the random returning starters?
The one piece of evidence you could post with no consequence and be immediately proven right when footage drops. So why wouldn’t they? Personally I think it’s because they don’t have the actual game and don’t want to claim what the starters are, because if they are wrong, they lose the ability to dangle having the game to their thirsty audience and any claim that they actually played the game.