Evolution makes things good enough, not perfect. But why?
If you were given an assignment would you work hard or work smart? Work smart is what our bodies did.
So if you already worked smart that should provide a scaffolding for working hard right? Why not make the model better if the structure is already in place? That doesn’t happen.
As time goes on we face new challenges, making us shift our focus from an ongoing work to a new project. Our bodies starts a new project for a new challenge, safely assuming that the other projects will protect the base.