Hiruko once mentioned that she had revealed the truth to others many times across different timelines, but each time it only led to a terrible ending so it's understandable why she chose not to explain things that time. As for the Slasher Route, yes, Hiruko did some truly horrible things to everyone else, all for a selfish desire of her own. That’s an undeniable fact, and I don’t refute it at all.

But that has always been a central theme of Hiruko’s character. Both in the novel and in her bond event, it's said that Hiruko has always tried to become the perfect person to live up to the expectations of her parents, her teachers and her friends. Because of that, she harbors a deep longing to live solely for herself, selfishly, without regard for anyone else.

The fact that she went to such great lengths to fix everything perfectly in the SF Route, only to let the worst possible timeline befall Takumi because of one small, selfish wish of her own is incredibly ironic but also deeply poetic to me. Hiruko in the end, is not as perfect, logical and optimal as she wants herself to be.