It's funny how the same complaints tech folks make of the construction industry are in parallel with what construction folks say of the tech industry. Both are based off ignorance. I have the pleasant curse of having a foot in both fields.
Real world construction is far more complex and difficult than what you imagine. Wide sweeping statements like, "incompetence of the construction companies and their governmental overseers" stinks of you having an cartoonish armchair understanding of what it actual takes from visualized computer renders to a real standing structure. Because civil engineering in the modern age has been a total failure, har har har. Honestly, it's people like you that are easily persuaded to vote for abolishing OSHA on the grounds to hasten construction times and lower costs. Because guess what, Cali construction costs are pretty high due to safety regulations. This is where... oh God forgive me for saying this... I agree with a lot of Cali construction code even though it can be excessive at times, it's warranted a lot of time. Especially because some of it is set for their specific region's character of obstacles... almost like local authorities know best and should enact laws how to construct depending on their local area's nuances! They shouldn't base their construction methods on regions from the other side of the planet!
The LGV route is a far more open and "flatter" (relatively speaking) than LA to SF. There's way less for them to tunnel or grade, which gets expensive quickly. HSR requires more gentle changes in direction than traditional rail. Building on flat, open terrain that no one is using is great... but that kind of terrain is already in use or owned by someone. Thus, easements or having to outright purchase the land. If not and you go for cheap land, it's going to come with downsides, like being mountainous.
At that, France sees less than 10 earthquake events over 2 magnitude a year on average. In the past week, there were already 6 events over 2 magnitude between LA and SF alone: https://www.cisn.org/map/index.html An LA to SF line is practically on a fault line. Devastating earthquakes are a real reality for a Cali line, not so much for France. The Cali standards for building rail are going to be higher than France, and for EXTREMELY good reason. Thus, price goes up for construction.
There's a lot more at play to building these things. What I mentioned barely scratches the surface to the complications. Claiming NIMBY is pretty naive if you don't take into consideration the real world problems and needs to achieving something compared to the lofty, idealistic wants of a project.