Why doesn't the US do something about that? China almost seems overt about stealing secrets like that.
Are you implying that the US are not actively doing the same against nations they see as a threat? It's basically how and why any intelligence service operates - know your enemy and keep up with their technological advances.
This has been true since the birth of the US. But the future may be different. China is advancing very fast through copying, and years from now we might stop thinking of them as a copycat.