What is easier is a Chinese company establishes a branch in the US that barely has any operation. But they then try to poach experienced Chinese-born workers in other US companies with high salary, good perks (paid travel to the Chinese HQ for example, who doesn't want to visit home and have the entire trip expensed?), generous PTO, etc.
They easily get the talents and industry knowledge from these hires. One person does not need to know or say everything, but a little piece from dozens of experienced employees coming from multiple industry leaders paint quite a comprehensive picture eventually.
And it is legal, and the participants can easily or unwillingly share critical information without raising any security flags since they are "protected" by the Chinese company. Any legal proceeding or investigations has to go through the corporation first so it is much more difficult for the US to handle these cases.