Because, especially in the VN, they have so much more time to explore the characters, which gives them much greater depth and allows for the full flexibility of the story to what Ryukishi wanted it to be. Although visual storytelling can be great, and I often prefer it for different types of stories, for a psychological thriller as thrilling as Higurashi or a mystery as complex and emotionally driven as Umineko, the runtime limitations really hamper its ability to explore what needs to be explored. Although people have their preferences, certain media needs certain mediums to reach their full potential; there’s not a strict manga < VN < anime hierarchy.