Because there are casualties. Dozens of CIA contacts in China have disappeared and a handful of US citizens and even CIA employees have been convicted of spying for China.
I mean if China found some traitors and detained or execute them why is this an espionage war? I am not convinced that this is related with the Huawei sanctions, it must be some economic or political strategy but I don't know what and why now and why with such a pathetic of excuse.