I think the argument is that it can't just be correlations because then we get stuck in the framework of the world looks as if things were going on before human

I think the argument is that it can't just be correlations because then we get stuck in the framework of the world looks as if things were going on before humans existed without being able to say that's true. Realists want to be able to say there are fossils in the ground because dinosaurs really did exist before us and not just that it appears that way to humans. Thus the speculative part of how to define reality in a way that isn't just correlated to our experiences.