Scary horror game SANATORIUM based on SLENDER

[Zaffre]

Never played Slenderman's Shadow (this game), but I have played Slender. I don't see why people keep making the same game. There's even Slender apps. I'm pretty sure Slender is copyrighted. It's blatantly obvious that the makers of these games stole the idea. When they've asked for money for an idea that wasn't theirs, wouldn't that be copyright infringement?