It does have an economic purpose, to enrich China. It also has geopolitical purpose, because China has been very keen to control our transportation infrastructure, starting with the Port of Long Beach,Pier J, way back in the day Ms Feinstein who has extensive ‘investments’ in China, approved.
It is spreading from there.
Your theory that China benefits most from California HSR is the best I’ve read of. I’ll bet you are right.