Because China can tell you “hey you don’t live here anymore” and plow right through neighborhoods and farms. Our property rights in the US are pretty absolute.
From a legal perspective eminent powers can be exercised quite efficiently. They haven't been exercised efficiently in California because of politics. HSR officials spend far too long haggling with farmers and pay much more than a court would require in an attempt to minimize negative media attention. But it has backfired by drawing things out and ballooning costs.
Only the first line was built in the 1960s.
The latest lines to be built are the Hokuriku Shinkansen (completed 1997-2015), Kyushu Shinkansen (built between 1991-2011) and the Hokkaido Shinkansen (construction strted 2005, still under construction). And of course the maglev Shinkansen has now started construction.
What? There is absolutely recourse, such as "sue them and at a minimum tie the project up in lawsuits for years". Or "be furious and rally with lots of other furious land owners/interested citizens and vote the bums out" because focused single interests, even as minorities, often can exert a great deal of political influence in a democracy. Or even illegally resisting through various means, which might not affect this area of California specifically but is a real threat in some parts of the US.
Eminent domain has an important place and has be used well, as well as abused. But whether justified or not its use, particularly in modern, is frequently fraught with controversy and political/legal battles.
The power as written is pretty powerful and has only gotten more powerful and broad every time it's challenged in court. Since it's hard to argue that building a high speed rail isn't "public use", the only thing you'd be suing over would be the "just compensation" part.
I believe in that case, the government can take and use first, and you can lawsuit afterwards over how much money you think it's worth which really doesn't stall anything.
If the government can use eminent domain successfully take over land to give to private developers to build a mall, or even take it just to increase city revenues, it sure as hell can use it to build a train.
"As a result, many states changed their eminent domain laws. Prior to the Kelo decision, only seven states specifically prohibited the use of eminent domain for economic development except to eliminate blight. Since the decision, forty-five states have amended their eminent domain laws, although some of these changes are cosmetic"
And in the end, they didn't even use her property as intended:
"In spite of repeated efforts, the redeveloper (who stood to get a 91-acre (370,000 m2) waterfront tract of land for $1 per year)[citation needed] was unable to obtain financing, and the redevelopment project was abandoned. As of the beginning of 2010, the original Kelo property was a vacant lot, generating no tax revenue for the city.[2] In the aftermath of 2011's Hurricane Irene, the now-closed New London redevelopment area was turned into a dump for storm debris such as tree branches and other vegetation."
Likewise, in American areas with good rail transport, you see business boom around it. The net gain in commerce, sales tax revenue, etc. cannot easily be measured, but it's significant and American could benefit greatly with better rail transport. You'd see America begin to collapse in and become less spread out within less than 50 years (especially in urban spaces).