ELI5: How did Konami lose the source code for the original Silent Hill game? Why couldn't they just datamine the source code from the retail copies of the game?

I've heard many times that the reason the Silent Hill remaster collection didn't turn out so well was because Konami lost the original source code and had to re-create it. But I don't understand how that is possible. If they were selling copies of Silent Hill, why couldn't they just take a single disk of it and datamine the source code off of it? How could they possess the game without possessing the game's source code?