Would you get tried in the US for interning at a company and then go to a competitor with all your inside knowledge ? [edit: barring a paid non compete agreement]
Then a step further from that, sure there are laws to prevent you from wholesale lifting corporate data and bringing them out as you leave, but as many laws it will be extremely difficult to detect and prove that happened in many low profile cases. That's why instead of just relying on the law you'll lock usb ports monitor network activity and get laptops returned when someone leaves.
It's kinda like preventing shop lifting, you know it will happen at some scale.
> US company / Chinese gov
How much leverage do you thing a Chinese company has to if a three letter US agency spies on them and pass the info to US companies ? And would you argue that scenario wouldn't happen if a specific Chinese company had a decisive advantage that could severly hurt US interests ?