You might recall California has a long history of employing Chinese immigrants for railroad construction.
In modern times, the biggest obstacle to new train routes tends to be acquiring the right of way. You generally have to buy up all the property in the path, or compensate people, and deal with the politics/lawsuits that generates. There are a number of public documents about programs for the high speed rail project: http://www.hsr.ca.gov/Programs/private_property.html
The Buy America Act is some of the problem, AFAIK. There's going to have to be a fair amount of training and construction of manufacturing sites for what is ultimately going to be relatively small orders, unless further HSR is built in the US.
But, vitally, they didn't want to deal with all the politics of the routeing. Large infrastructure projects are always in large part down to politics, potentially to their detriment (in this case, the business case being weakened by higher construction costs and slower end-to-end journeys leading to less keen private investors).
In modern times, the biggest obstacle to new train routes tends to be acquiring the right of way. You generally have to buy up all the property in the path, or compensate people, and deal with the politics/lawsuits that generates. There are a number of public documents about programs for the high speed rail project: http://www.hsr.ca.gov/Programs/private_property.html