A starting note: I don't disagree with you (about systemic issues), but I want to explain what I understand as the perspective you are responding to.

A "scapegoat" is someone who is incorrectly blamed for someone else's errors or sins. The perspective you're responding to is this: They built the system, they run the system, they have continuously warned "This system is dangerous!", and yet persisted. That is not being incorrectly blamed, not being a scapegoat, and instead is a collaborator.

So I think you mean to ask: "Why do people focus so much on finding someone to blame?" It's not merely semantic, because the answer to that is more straightforward: Consistent accountability is a major factor in deterring bad behavior. It is not the only factor, but it is a major one.

That is my Steel Man understanding of the people searching for individual blame.