Actually I think that makes sense. Cornell and Columbia are difficult to be admitted cuz they both have small classes so that they are way more competitive. I have seen other competitors whose GT are 730 and gpa 3.9 still be rejected. So don't lose confidence and keep waiting for USC!
Based on your WL from WM. I doubt your spoken English is not that good to get admitted to higher-level ones. But still, you have very good offers. Congrats!